d4/dd7/ddaspk_8f_source.html

 C Work performed under the auspices of the U.S. Department of Energy

 C by Lawrence Livermore National Laboratory under contract number

 C W-7405-Eng-48.

 C

       SUBROUTINE ddaspk (RES, NEQ, T, Y, YPRIME, TOUT, INFO, RTOL, ATOL,

      *   IDID, RWORK, LRW, IWORK, LIW, RPAR, IPAR, JAC, PSOL)

 C

 C***BEGIN PROLOGUE  DDASPK

 C***DATE WRITTEN   890101   (YYMMDD)

 C***REVISION DATE  910624

 C***REVISION DATE  920929   (CJ in RES call, RES counter fix.)

 C***REVISION DATE  921215   (Warnings on poor iteration performance)

 C***REVISION DATE  921216   (NRMAX as optional input)

 C***REVISION DATE  930315   (Name change: DDINI to DDINIT)

 C***REVISION DATE  940822   (Replaced initial condition calculation)

 C***REVISION DATE  941101   (Added linesearch in I.C. calculations)

 C***REVISION DATE  941220   (Misc. corrections throughout)

 C***REVISION DATE  950125   (Added DINVWT routine)

 C***REVISION DATE  950714   (Misc. corrections throughout)

 C***REVISION DATE  950802   (Default NRMAX = 5, based on tests.)

 C***REVISION DATE  950808   (Optional error test added.)

 C***REVISION DATE  950814   (Added I.C. constraints and INFO(14))

 C***REVISION DATE  950828   (Various minor corrections.)

 C***REVISION DATE  951006   (Corrected WT scaling in DFNRMK.)

 C***REVISION DATE  960129   (Corrected RL bug in DLINSD, DLINSK.)

 C***REVISION DATE  960301   (Added NONNEG to SAVE statement.)

 C***CATEGORY NO.  I1A2

 C***KEYWORDS  DIFFERENTIAL/ALGEBRAIC, BACKWARD DIFFERENTIATION FORMULAS,

 C             IMPLICIT DIFFERENTIAL SYSTEMS, KRYLOV ITERATION

 C***AUTHORS   Linda R. Petzold, Peter N. Brown, Alan C. Hindmarsh, and

 C                  Clement W. Ulrich

 C             Center for Computational Sciences & Engineering, L-316

 C             Lawrence Livermore National Laboratory

 C             P.O. Box 808,

 C             Livermore, CA 94551

 C***PURPOSE  This code solves a system of differential/algebraic

 C            equations of the form

 C               G(t,y,y') = 0 ,

 C            using a combination of Backward Differentiation Formula

 C            (BDF) methods and a choice of two linear system solution

 C            methods: direct (dense or band) or Krylov (iterative).

 C            This version is in double precision.

 C-----------------------------------------------------------------------

 C***DESCRIPTION

 C

 C *Usage:

 C

 C      IMPLICIT DOUBLE PRECISION(A-H,O-Z)

 C      INTEGER NEQ, INFO(N), IDID, LRW, LIW, IWORK(LIW), IPAR(*)

 C      DOUBLE PRECISION T, Y(*), YPRIME(*), TOUT, RTOL(*), ATOL(*),

 C         RWORK(LRW), RPAR(*)

 C      EXTERNAL  RES, JAC, PSOL

 C

 C      CALL DDASPK (RES, NEQ, T, Y, YPRIME, TOUT, INFO, RTOL, ATOL,

 C     *   IDID, RWORK, LRW, IWORK, LIW, RPAR, IPAR, JAC, PSOL)

 C

 C  Quantities which may be altered by the code are:

 C     T, Y(*), YPRIME(*), INFO(*), RTOL, ATOL, IDID, RWORK(*), IWORK(*)

 C

 C

 C *Arguments:

 C

 C  RES:EXT          This is the name of a subroutine which you

 C                   provide to define the residual function G(t,y,y')

 C                   of the differential/algebraic system.

 C

 C  NEQ:IN           This is the number of equations in the system.

 C

 C  T:INOUT          This is the current value of the independent

 C                   variable.

 C

 C  Y(*):INOUT       This array contains the solution components at T.

 C

 C  YPRIME(*):INOUT  This array contains the derivatives of the solution

 C                   components at T.

 C

 C  TOUT:IN          This is a point at which a solution is desired.

 C

 C  INFO(N):IN       This is an integer array used to communicate details

 C                   of how the solution is to be carried out, such as

 C                   tolerance type, matrix structure, step size and

 C                   order limits, and choice of nonlinear system method.

 C                   N must be at least 20.

 C

 C  RTOL,ATOL:INOUT  These quantities represent absolute and relative

 C                   error tolerances (on local error) which you provide

 C                   to indicate how accurately you wish the solution to

 C                   be computed.  You may choose them to be both scalars

 C                   or else both arrays of length NEQ.

 C

 C  IDID:OUT         This integer scalar is an indicator reporting what

 C                   the code did.  You must monitor this variable to

 C                   decide what action to take next.

 C

 C  RWORK:WORK       A real work array of length LRW which provides the

 C                   code with needed storage space.

 C

 C  LRW:IN           The length of RWORK.

 C

 C  IWORK:WORK       An integer work array of length LIW which provides

 C                   the code with needed storage space.

 C

 C  LIW:IN           The length of IWORK.

 C

 C  RPAR,IPAR:IN     These are real and integer parameter arrays which

 C                   you can use for communication between your calling

 C                   program and the RES, JAC, and PSOL subroutines.

 C

 C  JAC:EXT          This is the name of a subroutine which you may

 C                   provide (optionally) for calculating Jacobian

 C                   (partial derivative) data involved in solving linear

 C                   systems within DDASPK.

 C

 C  PSOL:EXT         This is the name of a subroutine which you must

 C                   provide for solving linear systems if you selected

 C                   a Krylov method.  The purpose of PSOL is to solve

 C                   linear systems involving a left preconditioner P.

 C

 C *Overview

 C

 C  The DDASPK solver uses the backward differentiation formulas of

 C  orders one through five to solve a system of the form G(t,y,y') = 0

 C  for y = Y and y' = YPRIME.  Values for Y and YPRIME at the initial

 C  time must be given as input.  These values should be consistent,

 C  that is, if T, Y, YPRIME are the given initial values, they should

 C  satisfy G(T,Y,YPRIME) = 0.  However, if consistent values are not

 C  known, in many cases you can have DDASPK solve for them -- see INFO(11).

 C  (This and other options are described in more detail below.)

 C

 C  Normally, DDASPK solves the system from T to TOUT.  It is easy to

 C  continue the solution to get results at additional TOUT.  This is

 C  the interval mode of operation.  Intermediate results can also be

 C  obtained easily by specifying INFO(3).

 C

 C  On each step taken by DDASPK, a sequence of nonlinear algebraic

 C  systems arises.  These are solved by one of two types of

 C  methods:

 C    * a Newton iteration with a direct method for the linear

 C      systems involved (INFO(12) = 0), or

 C    * a Newton iteration with a preconditioned Krylov iterative

 C      method for the linear systems involved (INFO(12) = 1).

 C

 C  The direct method choices are dense and band matrix solvers,

 C  with either a user-supplied or an internal difference quotient

 C  Jacobian matrix, as specified by INFO(5) and INFO(6).

 C  In the band case, INFO(6) = 1, you must supply half-bandwidths

 C  in IWORK(1) and IWORK(2).

 C

 C  The Krylov method is the Generalized Minimum Residual (GMRES)

 C  method, in either complete or incomplete form, and with

 C  scaling and preconditioning.  The method is implemented

 C  in an algorithm called SPIGMR.  Certain options in the Krylov

 C  method case are specified by INFO(13) and INFO(15).

 C

 C  If the Krylov method is chosen, you may supply a pair of routines,

 C  JAC and PSOL, to apply preconditioning to the linear system.

 C  If the system is A*x = b, the matrix is A = dG/dY + CJ*dG/dYPRIME

 C  (of order NEQ).  This system can then be preconditioned in the form

 C  (P-inverse)*A*x = (P-inverse)*b, with left preconditioner P.

 C  (DDASPK does not allow right preconditioning.)

 C  Then the Krylov method is applied to this altered, but equivalent,

 C  linear system, hopefully with much better performance than without

 C  preconditioning.  (In addition, a diagonal scaling matrix based on

 C  the tolerances is also introduced into the altered system.)

 C

 C  The JAC routine evaluates any data needed for solving systems

 C  with coefficient matrix P, and PSOL carries out that solution.

 C  In any case, in order to improve convergence, you should try to

 C  make P approximate the matrix A as much as possible, while keeping

 C  the system P*x = b reasonably easy and inexpensive to solve for x,

 C  given a vector b.

 C

 C

 C *Description

 C

 C------INPUT - WHAT TO DO ON THE FIRST CALL TO DDASPK-------------------

 C

 C

 C  The first call of the code is defined to be the start of each new

 C  problem.  Read through the descriptions of all the following items,

 C  provide sufficient storage space for designated arrays, set

 C  appropriate variables for the initialization of the problem, and

 C  give information about how you want the problem to be solved.

 C

 C

 C  RES -- Provide a subroutine of the form

 C

 C             SUBROUTINE RES (T, Y, YPRIME, CJ, DELTA, IRES, RPAR, IPAR)

 C

 C         to define the system of differential/algebraic

 C         equations which is to be solved. For the given values

 C         of T, Y and YPRIME, the subroutine should return

 C         the residual of the differential/algebraic system

 C             DELTA = G(T,Y,YPRIME)

 C         DELTA is a vector of length NEQ which is output from RES.

 C

 C         Subroutine RES must not alter T, Y, YPRIME, or CJ.

 C         You must declare the name RES in an EXTERNAL

 C         statement in your program that calls DDASPK.

 C         You must dimension Y, YPRIME, and DELTA in RES.

 C

 C         The input argument CJ can be ignored, or used to rescale

 C         constraint equations in the system (see Ref. 2, p. 145).

 C         Note: In this respect, DDASPK is not downward-compatible

 C         with DDASSL, which does not have the RES argument CJ.

 C

 C         IRES is an integer flag which is always equal to zero

 C         on input.  Subroutine RES should alter IRES only if it

 C         encounters an illegal value of Y or a stop condition.

 C         Set IRES = -1 if an input value is illegal, and DDASPK

 C         will try to solve the problem without getting IRES = -1.

 C         If IRES = -2, DDASPK will return control to the calling

 C         program with IDID = -11.

 C

 C         RPAR and IPAR are real and integer parameter arrays which

 C         you can use for communication between your calling program

 C         and subroutine RES. They are not altered by DDASPK. If you

 C         do not need RPAR or IPAR, ignore these parameters by treat-

 C         ing them as dummy arguments. If you do choose to use them,

 C         dimension them in your calling program and in RES as arrays

 C         of appropriate length.

 C

 C  NEQ -- Set it to the number of equations in the system (NEQ .GE. 1).

 C

 C  T -- Set it to the initial point of the integration. (T must be

 C       a variable.)

 C

 C  Y(*) -- Set this array to the initial values of the NEQ solution

 C          components at the initial point.  You must dimension Y of

 C          length at least NEQ in your calling program.

 C

 C  YPRIME(*) -- Set this array to the initial values of the NEQ first

 C               derivatives of the solution components at the initial

 C               point.  You must dimension YPRIME at least NEQ in your

 C               calling program.

 C

 C  TOUT - Set it to the first point at which a solution is desired.

 C         You cannot take TOUT = T.  Integration either forward in T

 C         (TOUT .GT. T) or backward in T (TOUT .LT. T) is permitted.

 C

 C         The code advances the solution from T to TOUT using step

 C         sizes which are automatically selected so as to achieve the

 C         desired accuracy.  If you wish, the code will return with the

 C         solution and its derivative at intermediate steps (the

 C         intermediate-output mode) so that you can monitor them,

 C         but you still must provide TOUT in accord with the basic

 C         aim of the code.

 C

 C         The first step taken by the code is a critical one because

 C         it must reflect how fast the solution changes near the

 C         initial point.  The code automatically selects an initial

 C         step size which is practically always suitable for the

 C         problem.  By using the fact that the code will not step past

 C         TOUT in the first step, you could, if necessary, restrict the

 C         length of the initial step.

 C

 C         For some problems it may not be permissible to integrate

 C         past a point TSTOP, because a discontinuity occurs there

 C         or the solution or its derivative is not defined beyond

 C         TSTOP.  When you have declared a TSTOP point (see INFO(4)

 C         and RWORK(1)), you have told the code not to integrate past

 C         TSTOP.  In this case any tout beyond TSTOP is invalid input.

 C

 C  INFO(*) - Use the INFO array to give the code more details about

 C            how you want your problem solved.  This array should be

 C            dimensioned of length 20, though DDASPK uses only the

 C            first 15 entries.  You must respond to all of the following

 C            items, which are arranged as questions.  The simplest use

 C            of DDASPK corresponds to setting all entries of INFO to 0.

 C

 C       INFO(1) - This parameter enables the code to initialize itself.

 C              You must set it to indicate the start of every new

 C              problem.

 C

 C          **** Is this the first call for this problem ...

 C                yes - set INFO(1) = 0

 C                 no - not applicable here.

 C                      See below for continuation calls.  ****

 C

 C       INFO(2) - How much accuracy you want of your solution

 C              is specified by the error tolerances RTOL and ATOL.

 C              The simplest use is to take them both to be scalars.

 C              To obtain more flexibility, they can both be arrays.

 C              The code must be told your choice.

 C

 C          **** Are both error tolerances RTOL, ATOL scalars ...

 C                yes - set INFO(2) = 0

 C                      and input scalars for both RTOL and ATOL

 C                 no - set INFO(2) = 1

 C                      and input arrays for both RTOL and ATOL ****

 C

 C       INFO(3) - The code integrates from T in the direction of TOUT

 C              by steps.  If you wish, it will return the computed

 C              solution and derivative at the next intermediate step

 C              (the intermediate-output mode) or TOUT, whichever comes

 C              first.  This is a good way to proceed if you want to

 C              see the behavior of the solution.  If you must have

 C              solutions at a great many specific TOUT points, this

 C              code will compute them efficiently.

 C

 C          **** Do you want the solution only at

 C               TOUT (and not at the next intermediate step) ...

 C                yes - set INFO(3) = 0

 C                 no - set INFO(3) = 1 ****

 C

 C       INFO(4) - To handle solutions at a great many specific

 C              values TOUT efficiently, this code may integrate past

 C              TOUT and interpolate to obtain the result at TOUT.

 C              Sometimes it is not possible to integrate beyond some

 C              point TSTOP because the equation changes there or it is

 C              not defined past TSTOP.  Then you must tell the code

 C              this stop condition.

 C

 C           **** Can the integration be carried out without any

 C                restrictions on the independent variable T ...

 C                 yes - set INFO(4) = 0

 C                  no - set INFO(4) = 1

 C                       and define the stopping point TSTOP by

 C                       setting RWORK(1) = TSTOP ****

 C

 C       INFO(5) - used only when INFO(12) = 0 (direct methods).

 C              To solve differential/algebraic systems you may wish

 C              to use a matrix of partial derivatives of the

 C              system of differential equations.  If you do not

 C              provide a subroutine to evaluate it analytically (see

 C              description of the item JAC in the call list), it will

 C              be approximated by numerical differencing in this code.

 C              Although it is less trouble for you to have the code

 C              compute partial derivatives by numerical differencing,

 C              the solution will be more reliable if you provide the

 C              derivatives via JAC.  Usually numerical differencing is

 C              more costly than evaluating derivatives in JAC, but

 C              sometimes it is not - this depends on your problem.

 C

 C           **** Do you want the code to evaluate the partial deriv-

 C                atives automatically by numerical differences ...

 C                 yes - set INFO(5) = 0

 C                  no - set INFO(5) = 1

 C                       and provide subroutine JAC for evaluating the

 C                       matrix of partial derivatives ****

 C

 C       INFO(6) - used only when INFO(12) = 0 (direct methods).

 C              DDASPK will perform much better if the matrix of

 C              partial derivatives, dG/dY + CJ*dG/dYPRIME (here CJ is

 C              a scalar determined by DDASPK), is banded and the code

 C              is told this.  In this case, the storage needed will be

 C              greatly reduced, numerical differencing will be performed

 C              much cheaper, and a number of important algorithms will

 C              execute much faster.  The differential equation is said

 C              to have half-bandwidths ML (lower) and MU (upper) if

 C              equation i involves only unknowns Y(j) with

 C                             i-ML .le. j .le. i+MU .

 C              For all i=1,2,...,NEQ.  Thus, ML and MU are the widths

 C              of the lower and upper parts of the band, respectively,

 C              with the main diagonal being excluded.  If you do not

 C              indicate that the equation has a banded matrix of partial

 C              derivatives the code works with a full matrix of NEQ**2

 C              elements (stored in the conventional way).  Computations

 C              with banded matrices cost less time and storage than with

 C              full matrices if  2*ML+MU .lt. NEQ.  If you tell the

 C              code that the matrix of partial derivatives has a banded

 C              structure and you want to provide subroutine JAC to

 C              compute the partial derivatives, then you must be careful

 C              to store the elements of the matrix in the special form

 C              indicated in the description of JAC.

 C

 C          **** Do you want to solve the problem using a full (dense)

 C               matrix (and not a special banded structure) ...

 C                yes - set INFO(6) = 0

 C                 no - set INFO(6) = 1

 C                       and provide the lower (ML) and upper (MU)

 C                       bandwidths by setting

 C                       IWORK(1)=ML

 C                       IWORK(2)=MU ****

 C

 C       INFO(7) - You can specify a maximum (absolute value of)

 C              stepsize, so that the code will avoid passing over very

 C              large regions.

 C

 C          ****  Do you want the code to decide on its own the maximum

 C                stepsize ...

 C                 yes - set INFO(7) = 0

 C                  no - set INFO(7) = 1

 C                       and define HMAX by setting

 C                       RWORK(2) = HMAX ****

 C

 C       INFO(8) -  Differential/algebraic problems may occasionally

 C              suffer from severe scaling difficulties on the first

 C              step.  If you know a great deal about the scaling of

 C              your problem, you can help to alleviate this problem

 C              by specifying an initial stepsize H0.

 C

 C          ****  Do you want the code to define its own initial

 C                stepsize ...

 C                 yes - set INFO(8) = 0

 C                  no - set INFO(8) = 1

 C                       and define H0 by setting

 C                       RWORK(3) = H0 ****

 C

 C       INFO(9) -  If storage is a severe problem, you can save some

 C              storage by restricting the maximum method order MAXORD.

 C              The default value is 5.  For each order decrease below 5,

 C              the code requires NEQ fewer locations, but it is likely

 C              to be slower.  In any case, you must have

 C              1 .le. MAXORD .le. 5.

 C          ****  Do you want the maximum order to default to 5 ...

 C                 yes - set INFO(9) = 0

 C                  no - set INFO(9) = 1

 C                       and define MAXORD by setting

 C                       IWORK(3) = MAXORD ****

 C

 C       INFO(10) - If you know that certain components of the

 C              solutions to your equations are always nonnegative

 C              (or nonpositive), it may help to set this

 C              parameter.  There are three options that are

 C              available:

 C              1.  To have constraint checking only in the initial

 C                  condition calculation.

 C              2.  To enforce nonnegativity in Y during the integration.

 C              3.  To enforce both options 1 and 2.

 C

 C              When selecting option 2 or 3, it is probably best to try the

 C              code without using this option first, and only use

 C              this option if that does not work very well.

 C

 C          ****  Do you want the code to solve the problem without

 C                invoking any special inequality constraints ...

 C                 yes - set INFO(10) = 0

 C                  no - set INFO(10) = 1 to have option 1 enforced

 C                  no - set INFO(10) = 2 to have option 2 enforced

 C                  no - set INFO(10) = 3 to have option 3 enforced ****

 C

 C                  If you have specified INFO(10) = 1 or 3, then you

 C                  will also need to identify how each component of Y

 C                  in the initial condition calculation is constrained.

 C                  You must set:

 C                  IWORK(40+I) = +1 if Y(I) must be .GE. 0,

 C                  IWORK(40+I) = +2 if Y(I) must be .GT. 0,

 C                  IWORK(40+I) = -1 if Y(I) must be .LE. 0, while

 C                  IWORK(40+I) = -2 if Y(I) must be .LT. 0, while

 C                  IWORK(40+I) =  0 if Y(I) is not constrained.

 C

 C       INFO(11) - DDASPK normally requires the initial T, Y, and

 C              YPRIME to be consistent.  That is, you must have

 C              G(T,Y,YPRIME) = 0 at the initial T.  If you do not know

 C              the initial conditions precisely, in some cases

 C              DDASPK may be able to compute it.

 C

 C              Denoting the differential variables in Y by Y_d

 C              and the algebraic variables by Y_a, DDASPK can solve

 C              one of two initialization problems:

 C              1.  Given Y_d, calculate Y_a and Y'_d, or

 C              2.  Given Y', calculate Y.

 C              In either case, initial values for the given

 C              components are input, and initial guesses for

 C              the unknown components must also be provided as input.

 C

 C          ****  Are the initial T, Y, YPRIME consistent ...

 C

 C                 yes - set INFO(11) = 0

 C                  no - set INFO(11) = 1 to calculate option 1 above,

 C                    or set INFO(11) = 2 to calculate option 2 ****

 C

 C                  If you have specified INFO(11) = 1, then you

 C                  will also need to identify  which are the

 C                  differential and which are the algebraic

 C                  components (algebraic components are components

 C                  whose derivatives do not appear explicitly

 C                  in the function G(T,Y,YPRIME)).  You must set:

 C                  IWORK(LID+I) = +1 if Y(I) is a differential variable

 C                  IWORK(LID+I) = -1 if Y(I) is an algebraic variable,

 C                  where LID = 40 if INFO(10) = 0 or 2 and LID = 40+NEQ

 C                  if INFO(10) = 1 or 3.

 C

 C       INFO(12) - Except for the addition of the RES argument CJ,

 C              DDASPK by default is downward-compatible with DDASSL,

 C              which uses only direct (dense or band) methods to solve

 C              the linear systems involved.  You must set INFO(12) to

 C              indicate whether you want the direct methods or the

 C              Krylov iterative method.

 C          ****   Do you want DDASPK to use standard direct methods

 C                 (dense or band) or the Krylov (iterative) method ...

 C                   direct methods - set INFO(12) = 0.

 C                   Krylov method  - set INFO(12) = 1,

 C                       and check the settings of INFO(13) and INFO(15).

 C

 C       INFO(13) - used when INFO(12) = 1 (Krylov methods).

 C              DDASPK uses scalars MAXL, KMP, NRMAX, and EPLI for the

 C              iterative solution of linear systems.  INFO(13) allows

 C              you to override the default values of these parameters.

 C              These parameters and their defaults are as follows:

 C              MAXL = maximum number of iterations in the SPIGMR

 C                 algorithm (MAXL .le. NEQ).  The default is

 C                 MAXL = MIN(5,NEQ).

 C              KMP = number of vectors on which orthogonalization is

 C                 done in the SPIGMR algorithm.  The default is

 C                 KMP = MAXL, which corresponds to complete GMRES

 C                 iteration, as opposed to the incomplete form.

 C              NRMAX = maximum number of restarts of the SPIGMR

 C                 algorithm per nonlinear iteration.  The default is

 C                 NRMAX = 5.

 C              EPLI = convergence test constant in SPIGMR algorithm.

 C                 The default is EPLI = 0.05.

 C              Note that the length of RWORK depends on both MAXL

 C              and KMP.  See the definition of LRW below.

 C          ****   Are MAXL, KMP, and EPLI to be given their

 C                 default values ...

 C                  yes - set INFO(13) = 0

 C                   no - set INFO(13) = 1,

 C                        and set all of the following:

 C                        IWORK(24) = MAXL (1 .le. MAXL .le. NEQ)

 C                        IWORK(25) = KMP  (1 .le. KMP .le. MAXL)

 C                        IWORK(26) = NRMAX  (NRMAX .ge. 0)

 C                        RWORK(10) = EPLI (0 .lt. EPLI .lt. 1.0) ****

 C

 C        INFO(14) - used with INFO(11) > 0 (initial condition

 C               calculation is requested).  In this case, you may

 C               request control to be returned to the calling program

 C               immediately after the initial condition calculation,

 C               before proceeding to the integration of the system

 C               (e.g. to examine the computed Y and YPRIME).

 C               If this is done, and if the initialization succeeded

 C               (IDID = 4), you should reset INFO(11) to 0 for the

 C               next call, to prevent the solver from repeating the

 C               initialization (and to avoid an infinite loop).

 C          ****   Do you want to proceed to the integration after

 C                 the initial condition calculation is done ...

 C                 yes - set INFO(14) = 0

 C                  no - set INFO(14) = 1                        ****

 C

 C        INFO(15) - used when INFO(12) = 1 (Krylov methods).

 C               When using preconditioning in the Krylov method,

 C               you must supply a subroutine, PSOL, which solves the

 C               associated linear systems using P.

 C               The usage of DDASPK is simpler if PSOL can carry out

 C               the solution without any prior calculation of data.

 C               However, if some partial derivative data is to be

 C               calculated in advance and used repeatedly in PSOL,

 C               then you must supply a JAC routine to do this,

 C               and set INFO(15) to indicate that JAC is to be called

 C               for this purpose.  For example, P might be an

 C               approximation to a part of the matrix A which can be

 C               calculated and LU-factored for repeated solutions of

 C               the preconditioner system.  The arrays WP and IWP

 C               (described under JAC and PSOL) can be used to

 C               communicate data between JAC and PSOL.

 C          ****   Does PSOL operate with no prior preparation ...

 C                 yes - set INFO(15) = 0 (no JAC routine)

 C                  no - set INFO(15) = 1

 C                       and supply a JAC routine to evaluate and

 C                       preprocess any required Jacobian data.  ****

 C

 C         INFO(16) - option to exclude algebraic variables from

 C               the error test.

 C          ****   Do you wish to control errors locally on

 C                 all the variables...

 C                 yes - set INFO(16) = 0

 C                  no - set INFO(16) = 1

 C                       If you have specified INFO(16) = 1, then you

 C                       will also need to identify  which are the

 C                       differential and which are the algebraic

 C                       components (algebraic components are components

 C                       whose derivatives do not appear explicitly

 C                       in the function G(T,Y,YPRIME)).  You must set:

 C                       IWORK(LID+I) = +1 if Y(I) is a differential

 C                                      variable, and

 C                       IWORK(LID+I) = -1 if Y(I) is an algebraic

 C                                      variable,

 C                       where LID = 40 if INFO(10) = 0 or 2 and

 C                       LID = 40 + NEQ if INFO(10) = 1 or 3.

 C

 C       INFO(17) - used when INFO(11) > 0 (DDASPK is to do an

 C              initial condition calculation).

 C              DDASPK uses several heuristic control quantities in the

 C              initial condition calculation.  They have default values,

 C              but can  also be set by the user using INFO(17).

 C              These parameters and their defaults are as follows:

 C              MXNIT  = maximum number of Newton iterations

 C                 per Jacobian or preconditioner evaluation.

 C                 The default is:

 C                 MXNIT =  5 in the direct case (INFO(12) = 0), and

 C                 MXNIT = 15 in the Krylov case (INFO(12) = 1).

 C              MXNJ   = maximum number of Jacobian or preconditioner

 C                 evaluations.  The default is:

 C                 MXNJ = 6 in the direct case (INFO(12) = 0), and

 C                 MXNJ = 2 in the Krylov case (INFO(12) = 1).

 C              MXNH   = maximum number of values of the artificial

 C                 stepsize parameter H to be tried if INFO(11) = 1.

 C                 The default is MXNH = 5.

 C                 NOTE: the maximum number of Newton iterations

 C                 allowed in all is MXNIT*MXNJ*MXNH if INFO(11) = 1,

 C                 and MXNIT*MXNJ if INFO(11) = 2.

 C              LSOFF  = flag to turn off the linesearch algorithm

 C                 (LSOFF = 0 means linesearch is on, LSOFF = 1 means

 C                 it is turned off).  The default is LSOFF = 0.

 C              STPTOL = minimum scaled step in linesearch algorithm.

 C                 The default is STPTOL = (unit roundoff)**(2/3).

 C              EPINIT = swing factor in the Newton iteration convergence

 C                 test.  The test is applied to the residual vector,

 C                 premultiplied by the approximate Jacobian (in the

 C                 direct case) or the preconditioner (in the Krylov

 C                 case).  For convergence, the weighted RMS norm of

 C                 this vector (scaled by the error weights) must be

 C                 less than EPINIT*EPCON, where EPCON = .33 is the

 C                 analogous test constant used in the time steps.

 C                 The default is EPINIT = .01.

 C          ****   Are the initial condition heuristic controls to be

 C                 given their default values...

 C                  yes - set INFO(17) = 0

 C                   no - set INFO(17) = 1,

 C                        and set all of the following:

 C                        IWORK(32) = MXNIT (.GT. 0)

 C                        IWORK(33) = MXNJ (.GT. 0)

 C                        IWORK(34) = MXNH (.GT. 0)

 C                        IWORK(35) = LSOFF ( = 0 or 1)

 C                        RWORK(14) = STPTOL (.GT. 0.0)

 C                        RWORK(15) = EPINIT (.GT. 0.0)  ****

 C

 C         INFO(18) - option to get extra printing in initial condition

 C                calculation.

 C          ****   Do you wish to have extra printing...

 C                 no  - set INFO(18) = 0

 C                 yes - set INFO(18) = 1 for minimal printing, or

 C                       set INFO(18) = 2 for full printing.

 C                       If you have specified INFO(18) .ge. 1, data

 C                       will be printed with the error handler routines.

 C                       To print to a non-default unit number L, include

 C                       the line  CALL XSETUN(L)  in your program.  ****

 C

 C   RTOL, ATOL -- You must assign relative (RTOL) and absolute (ATOL)

 C               error tolerances to tell the code how accurately you

 C               want the solution to be computed.  They must be defined

 C               as variables because the code may change them.

 C               you have two choices --

 C                     Both RTOL and ATOL are scalars (INFO(2) = 0), or

 C                     both RTOL and ATOL are vectors (INFO(2) = 1).

 C               In either case all components must be non-negative.

 C

 C               The tolerances are used by the code in a local error

 C               test at each step which requires roughly that

 C                        abs(local error in Y(i)) .le. EWT(i) ,

 C               where EWT(i) = RTOL*abs(Y(i)) + ATOL is an error weight

 C               quantity, for each vector component.

 C               (More specifically, a root-mean-square norm is used to

 C               measure the size of vectors, and the error test uses the

 C               magnitude of the solution at the beginning of the step.)

 C

 C               The true (global) error is the difference between the

 C               true solution of the initial value problem and the

 C               computed approximation.  Practically all present day

 C               codes, including this one, control the local error at

 C               each step and do not even attempt to control the global

 C               error directly.

 C

 C               Usually, but not always, the true accuracy of

 C               the computed Y is comparable to the error tolerances.

 C               This code will usually, but not always, deliver a more

 C               accurate solution if you reduce the tolerances and

 C               integrate again.  By comparing two such solutions you

 C               can get a fairly reliable idea of the true error in the

 C               solution at the larger tolerances.

 C

 C               Setting ATOL = 0. results in a pure relative error test

 C               on that component.  Setting RTOL = 0. results in a pure

 C               absolute error test on that component.  A mixed test

 C               with non-zero RTOL and ATOL corresponds roughly to a

 C               relative error test when the solution component is

 C               much bigger than ATOL and to an absolute error test

 C               when the solution component is smaller than the

 C               threshold ATOL.

 C

 C               The code will not attempt to compute a solution at an

 C               accuracy unreasonable for the machine being used.  It

 C               will advise you if you ask for too much accuracy and

 C               inform you as to the maximum accuracy it believes

 C               possible.

 C

 C  RWORK(*) -- a real work array, which should be dimensioned in your

 C               calling program with a length equal to the value of

 C               LRW (or greater).

 C

 C  LRW -- Set it to the declared length of the RWORK array.  The

 C               minimum length depends on the options you have selected,

 C               given by a base value plus additional storage as described

 C               below.

 C

 C               If INFO(12) = 0 (standard direct method), the base value is

 C               base = 50 + max(MAXORD+4,7)*NEQ.

 C               The default value is MAXORD = 5 (see INFO(9)).  With the

 C               default MAXORD, base = 50 + 9*NEQ.

 C               Additional storage must be added to the base value for

 C               any or all of the following options:

 C                 if INFO(6) = 0 (dense matrix), add NEQ**2

 C                 if INFO(6) = 1 (banded matrix), then

 C                    if INFO(5) = 0, add (2*ML+MU+1)*NEQ + 2*(NEQ/(ML+MU+1)+1),

 C                    if INFO(5) = 1, add (2*ML+MU+1)*NEQ,

 C                 if INFO(16) = 1, add NEQ.

 C

 C              If INFO(12) = 1 (Krylov method), the base value is

 C              base = 50 + (MAXORD+5)*NEQ + (MAXL+3+MIN0(1,MAXL-KMP))*NEQ +

 C                      + (MAXL+3)*MAXL + 1 + LENWP.

 C              See PSOL for description of LENWP.  The default values are:

 C              MAXORD = 5 (see INFO(9)), MAXL = min(5,NEQ) and KMP = MAXL

 C              (see INFO(13)).

 C              With the default values for MAXORD, MAXL and KMP,

 C              base = 91 + 18*NEQ + LENWP.

 C              Additional storage must be added to the base value for

 C              any or all of the following options:

 C                if INFO(16) = 1, add NEQ.

 C

 C

 C  IWORK(*) -- an integer work array, which should be dimensioned in

 C              your calling program with a length equal to the value

 C              of LIW (or greater).

 C

 C  LIW -- Set it to the declared length of the IWORK array.  The

 C             minimum length depends on the options you have selected,

 C             given by a base value plus additional storage as described

 C             below.

 C

 C             If INFO(12) = 0 (standard direct method), the base value is

 C             base = 40 + NEQ.

 C             IF INFO(10) = 1 or 3, add NEQ to the base value.

 C             If INFO(11) = 1 or INFO(16) =1, add NEQ to the base value.

 C

 C             If INFO(12) = 1 (Krylov method), the base value is

 C             base = 40 + LENIWP.

 C             See PSOL for description of LENIWP.

 C             IF INFO(10) = 1 or 3, add NEQ to the base value.

 C             If INFO(11) = 1 or INFO(16) = 1, add NEQ to the base value.

 C

 C

 C  RPAR, IPAR -- These are arrays of double precision and integer type,

 C             respectively, which are available for you to use

 C             for communication between your program that calls

 C             DDASPK and the RES subroutine (and the JAC and PSOL

 C             subroutines).  They are not altered by DDASPK.

 C             If you do not need RPAR or IPAR, ignore these

 C             parameters by treating them as dummy arguments.

 C             If you do choose to use them, dimension them in

 C             your calling program and in RES (and in JAC and PSOL)

 C             as arrays of appropriate length.

 C

 C  JAC -- This is the name of a routine that you may supply

 C         (optionally) that relates to the Jacobian matrix of the

 C         nonlinear system that the code must solve at each T step.

 C         The role of JAC (and its call sequence) depends on whether

 C         a direct (INFO(12) = 0) or Krylov (INFO(12) = 1) method

 C         is selected.

 C

 C         **** INFO(12) = 0 (direct methods):

 C           If you are letting the code generate partial derivatives

 C           numerically (INFO(5) = 0), then JAC can be absent

 C           (or perhaps a dummy routine to satisfy the loader).

 C           Otherwise you must supply a JAC routine to compute

 C           the matrix A = dG/dY + CJ*dG/dYPRIME.  It must have

 C           the form

 C

 C           SUBROUTINE JAC (T, Y, YPRIME, PD, CJ, RPAR, IPAR)

 C

 C           The JAC routine must dimension Y, YPRIME, and PD (and RPAR

 C           and IPAR if used).  CJ is a scalar which is input to JAC.

 C           For the given values of T, Y, and YPRIME, the JAC routine

 C           must evaluate the nonzero elements of the matrix A, and

 C           store these values in the array PD.  The elements of PD are

 C           set to zero before each call to JAC, so that only nonzero

 C           elements need to be defined.

 C           The way you store the elements into the PD array depends

 C           on the structure of the matrix indicated by INFO(6).

 C           *** INFO(6) = 0 (full or dense matrix) ***

 C               Give PD a first dimension of NEQ.  When you evaluate the

 C               nonzero partial derivatives of equation i (i.e. of G(i))

 C               with respect to component j (of Y and YPRIME), you must

 C               store the element in PD according to

 C                  PD(i,j) = dG(i)/dY(j) + CJ*dG(i)/dYPRIME(j).

 C           *** INFO(6) = 1 (banded matrix with half-bandwidths ML, MU

 C                            as described under INFO(6)) ***

 C               Give PD a first dimension of 2*ML+MU+1.  When you

 C               evaluate the nonzero partial derivatives of equation i

 C               (i.e. of G(i)) with respect to component j (of Y and

 C               YPRIME), you must store the element in PD according to

 C                  IROW = i - j + ML + MU + 1

 C                  PD(IROW,j) = dG(i)/dY(j) + CJ*dG(i)/dYPRIME(j).

 C

 C          **** INFO(12) = 1 (Krylov method):

 C            If you are not calculating Jacobian data in advance for use

 C            in PSOL (INFO(15) = 0), JAC can be absent (or perhaps a

 C            dummy routine to satisfy the loader).  Otherwise, you may

 C            supply a JAC routine to compute and preprocess any parts of

 C            of the Jacobian matrix  A = dG/dY + CJ*dG/dYPRIME that are

 C            involved in the preconditioner matrix P.

 C            It is to have the form

 C

 C            SUBROUTINE JAC (RES, IRES, NEQ, T, Y, YPRIME, REWT, SAVR,

 C                            WK, H, CJ, WP, IWP, IER, RPAR, IPAR)

 C

 C           The JAC routine must dimension Y, YPRIME, REWT, SAVR, WK,

 C           and (if used) WP, IWP, RPAR, and IPAR.

 C           The Y, YPRIME, and SAVR arrays contain the current values

 C           of Y, YPRIME, and the residual G, respectively.

 C           The array WK is work space of length NEQ.

 C           H is the step size.  CJ is a scalar, input to JAC, that is

 C           normally proportional to 1/H.  REWT is an array of

 C           reciprocal error weights, 1/EWT(i), where EWT(i) is

 C           RTOL*abs(Y(i)) + ATOL (unless you supplied routine DDAWTS

 C           instead), for use in JAC if needed.  For example, if JAC

 C           computes difference quotient approximations to partial

 C           derivatives, the REWT array may be useful in setting the

 C           increments used.  The JAC routine should do any

 C           factorization operations called for, in preparation for

 C           solving linear systems in PSOL.  The matrix P should

 C           be an approximation to the Jacobian,

 C           A = dG/dY + CJ*dG/dYPRIME.

 C

 C           WP and IWP are real and integer work arrays which you may

 C           use for communication between your JAC routine and your

 C           PSOL routine.  These may be used to store elements of the

 C           preconditioner P, or related matrix data (such as factored

 C           forms).  They are not altered by DDASPK.

 C           If you do not need WP or IWP, ignore these parameters by

 C           treating them as dummy arguments.  If you do use them,

 C           dimension them appropriately in your JAC and PSOL routines.

 C           See the PSOL description for instructions on setting

 C           the lengths of WP and IWP.

 C

 C           On return, JAC should set the error flag IER as follows..

 C             IER = 0    if JAC was successful,

 C             IER .ne. 0 if JAC was unsuccessful (e.g. if Y or YPRIME

 C                        was illegal, or a singular matrix is found).

 C           (If IER .ne. 0, a smaller stepsize will be tried.)

 C           IER = 0 on entry to JAC, so need be reset only on a failure.

 C           If RES is used within JAC, then a nonzero value of IRES will

 C           override any nonzero value of IER (see the RES description).

 C

 C         Regardless of the method type, subroutine JAC must not

 C         alter T, Y(*), YPRIME(*), H, CJ, or REWT(*).

 C         You must declare the name JAC in an EXTERNAL statement in

 C         your program that calls DDASPK.

 C

 C PSOL --  This is the name of a routine you must supply if you have

 C         selected a Krylov method (INFO(12) = 1) with preconditioning.

 C         In the direct case (INFO(12) = 0), PSOL can be absent

 C         (a dummy routine may have to be supplied to satisfy the

 C         loader).  Otherwise, you must provide a PSOL routine to

 C         solve linear systems arising from preconditioning.

 C         When supplied with INFO(12) = 1, the PSOL routine is to

 C         have the form

 C

 C         SUBROUTINE PSOL (NEQ, T, Y, YPRIME, SAVR, WK, CJ, WGHT,

 C                          WP, IWP, B, EPLIN, IER, RPAR, IPAR)

 C

 C         The PSOL routine must solve linear systems of the form

 C         P*x = b where P is the left preconditioner matrix.

 C

 C         The right-hand side vector b is in the B array on input, and

 C         PSOL must return the solution vector x in B.

 C         The Y, YPRIME, and SAVR arrays contain the current values

 C         of Y, YPRIME, and the residual G, respectively.

 C

 C         Work space required by JAC and/or PSOL, and space for data to

 C         be communicated from JAC to PSOL is made available in the form

 C         of arrays WP and IWP, which are parts of the RWORK and IWORK

 C         arrays, respectively.  The lengths of these real and integer

 C         work spaces WP and IWP must be supplied in LENWP and LENIWP,

 C         respectively, as follows..

 C           IWORK(27) = LENWP = length of real work space WP

 C           IWORK(28) = LENIWP = length of integer work space IWP.

 C

 C         WK is a work array of length NEQ for use by PSOL.

 C         CJ is a scalar, input to PSOL, that is normally proportional

 C         to 1/H (H = stepsize).  If the old value of CJ

 C         (at the time of the last JAC call) is needed, it must have

 C         been saved by JAC in WP.

 C

 C         WGHT is an array of weights, to be used if PSOL uses an

 C         iterative method and performs a convergence test.  (In terms

 C         of the argument REWT to JAC, WGHT is REWT/sqrt(NEQ).)

 C         If PSOL uses an iterative method, it should use EPLIN

 C         (a heuristic parameter) as the bound on the weighted norm of

 C         the residual for the computed solution.  Specifically, the

 C         residual vector R should satisfy

 C              SQRT (SUM ( (R(i)*WGHT(i))**2 ) ) .le. EPLIN

 C

 C         PSOL must not alter NEQ, T, Y, YPRIME, SAVR, CJ, WGHT, EPLIN.

 C

 C         On return, PSOL should set the error flag IER as follows..

 C           IER = 0 if PSOL was successful,

 C           IER .lt. 0 if an unrecoverable error occurred, meaning

 C                 control will be passed to the calling routine,

 C           IER .gt. 0 if a recoverable error occurred, meaning that

 C                 the step will be retried with the same step size

 C                 but with a call to JAC to update necessary data,

 C                 unless the Jacobian data is current, in which case

 C                 the step will be retried with a smaller step size.

 C           IER = 0 on entry to PSOL so need be reset only on a failure.

 C

 C         You must declare the name PSOL in an EXTERNAL statement in

 C         your program that calls DDASPK.

 C

 C

 C  OPTIONALLY REPLACEABLE SUBROUTINE:

 C

 C  DDASPK uses a weighted root-mean-square norm to measure the

 C  size of various error vectors.  The weights used in this norm

 C  are set in the following subroutine:

 C

 C    SUBROUTINE DDAWTS (NEQ, IWT, RTOL, ATOL, Y, EWT, RPAR, IPAR)

 C    DIMENSION RTOL(*), ATOL(*), Y(*), EWT(*), RPAR(*), IPAR(*)

 C

 C  A DDAWTS routine has been included with DDASPK which sets the

 C  weights according to

 C    EWT(I) = RTOL*ABS(Y(I)) + ATOL

 C  in the case of scalar tolerances (IWT = 0) or

 C    EWT(I) = RTOL(I)*ABS(Y(I)) + ATOL(I)

 C  in the case of array tolerances (IWT = 1).  (IWT is INFO(2).)

 C  In some special cases, it may be appropriate for you to define

 C  your own error weights by writing a subroutine DDAWTS to be

 C  called instead of the version supplied.  However, this should

 C  be attempted only after careful thought and consideration.

 C  If you supply this routine, you may use the tolerances and Y

 C  as appropriate, but do not overwrite these variables.  You

 C  may also use RPAR and IPAR to communicate data as appropriate.

 C  ***Note: Aside from the values of the weights, the choice of

 C  norm used in DDASPK (weighted root-mean-square) is not subject

 C  to replacement by the user.  In this respect, DDASPK is not

 C  downward-compatible with the original DDASSL solver (in which

 C  the norm routine was optionally user-replaceable).

 C

 C

 C------OUTPUT - AFTER ANY RETURN FROM DDASPK----------------------------

 C

 C  The principal aim of the code is to return a computed solution at

 C  T = TOUT, although it is also possible to obtain intermediate

 C  results along the way.  To find out whether the code achieved its

 C  goal or if the integration process was interrupted before the task

 C  was completed, you must check the IDID parameter.

 C

 C

 C   T -- The output value of T is the point to which the solution

 C        was successfully advanced.

 C

 C   Y(*) -- contains the computed solution approximation at T.

 C

 C   YPRIME(*) -- contains the computed derivative approximation at T.

 C

 C   IDID -- reports what the code did, described as follows:

 C

 C                     *** TASK COMPLETED ***

 C                Reported by positive values of IDID

 C

 C           IDID = 1 -- a step was successfully taken in the

 C                   intermediate-output mode.  The code has not

 C                   yet reached TOUT.

 C

 C           IDID = 2 -- the integration to TSTOP was successfully

 C                   completed (T = TSTOP) by stepping exactly to TSTOP.

 C

 C           IDID = 3 -- the integration to TOUT was successfully

 C                   completed (T = TOUT) by stepping past TOUT.

 C                   Y(*) and YPRIME(*) are obtained by interpolation.

 C

 C           IDID = 4 -- the initial condition calculation, with

 C                   INFO(11) > 0, was successful, and INFO(14) = 1.

 C                   No integration steps were taken, and the solution

 C                   is not considered to have been started.

 C

 C                    *** TASK INTERRUPTED ***

 C                Reported by negative values of IDID

 C

 C           IDID = -1 -- a large amount of work has been expended

 C                     (about 500 steps).

 C

 C           IDID = -2 -- the error tolerances are too stringent.

 C

 C           IDID = -3 -- the local error test cannot be satisfied

 C                     because you specified a zero component in ATOL

 C                     and the corresponding computed solution component

 C                     is zero.  Thus, a pure relative error test is

 C                     impossible for this component.

 C

 C           IDID = -5 -- there were repeated failures in the evaluation

 C                     or processing of the preconditioner (in JAC).

 C

 C           IDID = -6 -- DDASPK had repeated error test failures on the

 C                     last attempted step.

 C

 C           IDID = -7 -- the nonlinear system solver in the time integration

 C                     could not converge.

 C

 C           IDID = -8 -- the matrix of partial derivatives appears

 C                     to be singular (direct method).

 C

 C           IDID = -9 -- the nonlinear system solver in the time integration

 C                     failed to achieve convergence, and there were repeated

 C                     error test failures in this step.

 C

 C           IDID =-10 -- the nonlinear system solver in the time integration

 C                     failed to achieve convergence because IRES was equal

 C                     to -1.

 C

 C           IDID =-11 -- IRES = -2 was encountered and control is

 C                     being returned to the calling program.

 C

 C           IDID =-12 -- DDASPK failed to compute the initial Y, YPRIME.

 C

 C           IDID =-13 -- unrecoverable error encountered inside user's

 C                     PSOL routine, and control is being returned to

 C                     the calling program.

 C

 C           IDID =-14 -- the Krylov linear system solver could not

 C                     achieve convergence.

 C

 C           IDID =-15,..,-32 -- Not applicable for this code.

 C

 C                    *** TASK TERMINATED ***

 C                reported by the value of IDID=-33

 C

 C           IDID = -33 -- the code has encountered trouble from which

 C                   it cannot recover.  A message is printed

 C                   explaining the trouble and control is returned

 C                   to the calling program.  For example, this occurs

 C                   when invalid input is detected.

 C

 C   RTOL, ATOL -- these quantities remain unchanged except when

 C               IDID = -2.  In this case, the error tolerances have been

 C               increased by the code to values which are estimated to

 C               be appropriate for continuing the integration.  However,

 C               the reported solution at T was obtained using the input

 C               values of RTOL and ATOL.

 C

 C   RWORK, IWORK -- contain information which is usually of no interest

 C               to the user but necessary for subsequent calls.

 C               However, you may be interested in the performance data

 C               listed below.  These quantities are accessed in RWORK

 C               and IWORK but have internal mnemonic names, as follows..

 C

 C               RWORK(3)--contains H, the step size h to be attempted

 C                        on the next step.

 C

 C               RWORK(4)--contains TN, the current value of the

 C                        independent variable, i.e. the farthest point

 C                        integration has reached.  This will differ

 C                        from T if interpolation has been performed

 C                        (IDID = 3).

 C

 C               RWORK(7)--contains HOLD, the stepsize used on the last

 C                        successful step.  If INFO(11) = INFO(14) = 1,

 C                        this contains the value of H used in the

 C                        initial condition calculation.

 C

 C               IWORK(7)--contains K, the order of the method to be

 C                        attempted on the next step.

 C

 C               IWORK(8)--contains KOLD, the order of the method used

 C                        on the last step.

 C

 C               IWORK(11)--contains NST, the number of steps (in T)

 C                        taken so far.

 C

 C               IWORK(12)--contains NRE, the number of calls to RES

 C                        so far.

 C

 C               IWORK(13)--contains NJE, the number of calls to JAC so

 C                        far (Jacobian or preconditioner evaluations).

 C

 C               IWORK(14)--contains NETF, the total number of error test

 C                        failures so far.

 C

 C               IWORK(15)--contains NCFN, the total number of nonlinear

 C                        convergence failures so far (includes counts

 C                        of singular iteration matrix or singular

 C                        preconditioners).

 C

 C               IWORK(16)--contains NCFL, the number of convergence

 C                        failures of the linear iteration so far.

 C

 C               IWORK(17)--contains LENIW, the length of IWORK actually

 C                        required.  This is defined on normal returns

 C                        and on an illegal input return for

 C                        insufficient storage.

 C

 C               IWORK(18)--contains LENRW, the length of RWORK actually

 C                        required.  This is defined on normal returns

 C                        and on an illegal input return for

 C                        insufficient storage.

 C

 C               IWORK(19)--contains NNI, the total number of nonlinear

 C                        iterations so far (each of which calls a

 C                        linear solver).

 C

 C               IWORK(20)--contains NLI, the total number of linear

 C                        (Krylov) iterations so far.

 C

 C               IWORK(21)--contains NPS, the number of PSOL calls so

 C                        far, for preconditioning solve operations or

 C                        for solutions with the user-supplied method.

 C

 C               Note: The various counters in IWORK do not include

 C               counts during a call made with INFO(11) > 0 and

 C               INFO(14) = 1.

 C

 C

 C------INPUT - WHAT TO DO TO CONTINUE THE INTEGRATION  -----------------

 C              (CALLS AFTER THE FIRST)

 C

 C     This code is organized so that subsequent calls to continue the

 C     integration involve little (if any) additional effort on your

 C     part.  You must monitor the IDID parameter in order to determine

 C     what to do next.

 C

 C     Recalling that the principal task of the code is to integrate

 C     from T to TOUT (the interval mode), usually all you will need

 C     to do is specify a new TOUT upon reaching the current TOUT.

 C

 C     Do not alter any quantity not specifically permitted below.  In

 C     particular do not alter NEQ, T, Y(*), YPRIME(*), RWORK(*),

 C     IWORK(*), or the differential equation in subroutine RES.  Any

 C     such alteration constitutes a new problem and must be treated

 C     as such, i.e. you must start afresh.

 C

 C     You cannot change from array to scalar error control or vice

 C     versa (INFO(2)), but you can change the size of the entries of

 C     RTOL or ATOL.  Increasing a tolerance makes the equation easier

 C     to integrate.  Decreasing a tolerance will make the equation

 C     harder to integrate and should generally be avoided.

 C

 C     You can switch from the intermediate-output mode to the

 C     interval mode (INFO(3)) or vice versa at any time.

 C

 C     If it has been necessary to prevent the integration from going

 C     past a point TSTOP (INFO(4), RWORK(1)), keep in mind that the

 C     code will not integrate to any TOUT beyond the currently

 C     specified TSTOP.  Once TSTOP has been reached, you must change

 C     the value of TSTOP or set INFO(4) = 0.  You may change INFO(4)

 C     or TSTOP at any time but you must supply the value of TSTOP in

 C     RWORK(1) whenever you set INFO(4) = 1.

 C

 C     Do not change INFO(5), INFO(6), INFO(12-17) or their associated

 C     IWORK/RWORK locations unless you are going to restart the code.

 C

 C                    *** FOLLOWING A COMPLETED TASK ***

 C

 C     If..

 C     IDID = 1, call the code again to continue the integration

 C                  another step in the direction of TOUT.

 C

 C     IDID = 2 or 3, define a new TOUT and call the code again.

 C                  TOUT must be different from T.  You cannot change

 C                  the direction of integration without restarting.

 C

 C     IDID = 4, reset INFO(11) = 0 and call the code again to begin

 C                  the integration.  (If you leave INFO(11) > 0 and

 C                  INFO(14) = 1, you may generate an infinite loop.)

 C                  In this situation, the next call to DASPK is

 C                  considered to be the first call for the problem,

 C                  in that all initializations are done.

 C

 C                    *** FOLLOWING AN INTERRUPTED TASK ***

 C

 C     To show the code that you realize the task was interrupted and

 C     that you want to continue, you must take appropriate action and

 C     set INFO(1) = 1.

 C

 C     If..

 C     IDID = -1, the code has taken about 500 steps.  If you want to

 C                  continue, set INFO(1) = 1 and call the code again.

 C                  An additional 500 steps will be allowed.

 C

 C

 C     IDID = -2, the error tolerances RTOL, ATOL have been increased

 C                  to values the code estimates appropriate for

 C                  continuing.  You may want to change them yourself.

 C                  If you are sure you want to continue with relaxed

 C                  error tolerances, set INFO(1) = 1 and call the code

 C                  again.

 C

 C     IDID = -3, a solution component is zero and you set the

 C                  corresponding component of ATOL to zero.  If you

 C                  are sure you want to continue, you must first alter

 C                  the error criterion to use positive values of ATOL

 C                  for those components corresponding to zero solution

 C                  components, then set INFO(1) = 1 and call the code

 C                  again.

 C

 C     IDID = -4  --- cannot occur with this code.

 C

 C     IDID = -5, your JAC routine failed with the Krylov method.  Check

 C                  for errors in JAC and restart the integration.

 C

 C     IDID = -6, repeated error test failures occurred on the last

 C                  attempted step in DDASPK.  A singularity in the

 C                  solution may be present.  If you are absolutely

 C                  certain you want to continue, you should restart

 C                  the integration.  (Provide initial values of Y and

 C                  YPRIME which are consistent.)

 C

 C     IDID = -7, repeated convergence test failures occurred on the last

 C                  attempted step in DDASPK.  An inaccurate or ill-

 C                  conditioned Jacobian or preconditioner may be the

 C                  problem.  If you are absolutely certain you want

 C                  to continue, you should restart the integration.

 C

 C

 C     IDID = -8, the matrix of partial derivatives is singular, with

 C                  the use of direct methods.  Some of your equations

 C                  may be redundant.  DDASPK cannot solve the problem

 C                  as stated.  It is possible that the redundant

 C                  equations could be removed, and then DDASPK could

 C                  solve the problem.  It is also possible that a

 C                  solution to your problem either does not exist

 C                  or is not unique.

 C

 C     IDID = -9, DDASPK had multiple convergence test failures, preceded

 C                  by multiple error test failures, on the last

 C                  attempted step.  It is possible that your problem is

 C                  ill-posed and cannot be solved using this code.  Or,

 C                  there may be a discontinuity or a singularity in the

 C                  solution.  If you are absolutely certain you want to

 C                  continue, you should restart the integration.

 C

 C     IDID = -10, DDASPK had multiple convergence test failures

 C                  because IRES was equal to -1.  If you are

 C                  absolutely certain you want to continue, you

 C                  should restart the integration.

 C

 C     IDID = -11, there was an unrecoverable error (IRES = -2) from RES

 C                  inside the nonlinear system solver.  Determine the

 C                  cause before trying again.

 C

 C     IDID = -12, DDASPK failed to compute the initial Y and YPRIME

 C                  vectors.  This could happen because the initial

 C                  approximation to Y or YPRIME was not very good, or

 C                  because no consistent values of these vectors exist.

 C                  The problem could also be caused by an inaccurate or

 C                  singular iteration matrix, or a poor preconditioner.

 C

 C     IDID = -13, there was an unrecoverable error encountered inside

 C                  your PSOL routine.  Determine the cause before

 C                  trying again.

 C

 C     IDID = -14, the Krylov linear system solver failed to achieve

 C                  convergence.  This may be due to ill-conditioning

 C                  in the iteration matrix, or a singularity in the

 C                  preconditioner (if one is being used).

 C                  Another possibility is that there is a better

 C                  choice of Krylov parameters (see INFO(13)).

 C                  Possibly the failure is caused by redundant equations

 C                  in the system, or by inconsistent equations.

 C                  In that case, reformulate the system to make it

 C                  consistent and non-redundant.

 C

 C     IDID = -15,..,-32 --- Cannot occur with this code.

 C

 C                       *** FOLLOWING A TERMINATED TASK ***

 C

 C     If IDID = -33, you cannot continue the solution of this problem.

 C                  An attempt to do so will result in your run being

 C                  terminated.

 C

 C  ---------------------------------------------------------------------

 C

 C***REFERENCES

 C  1.  L. R. Petzold, A Description of DASSL: A Differential/Algebraic

 C      System Solver, in Scientific Computing, R. S. Stepleman et al.

 C      (Eds.), North-Holland, Amsterdam, 1983, pp. 65-68.

 C  2.  K. E. Brenan, S. L. Campbell, and L. R. Petzold, Numerical

 C      Solution of Initial-Value Problems in Differential-Algebraic

 C      Equations, Elsevier, New York, 1989.

 C  3.  P. N. Brown and A. C. Hindmarsh, Reduced Storage Matrix Methods

 C      in Stiff ODE Systems, J. Applied Mathematics and Computation,

 C      31 (1989), pp. 40-91.

 C  4.  P. N. Brown, A. C. Hindmarsh, and L. R. Petzold, Using Krylov

 C      Methods in the Solution of Large-Scale Differential-Algebraic

 C      Systems, SIAM J. Sci. Comp., 15 (1994), pp. 1467-1488.

 C  5.  P. N. Brown, A. C. Hindmarsh, and L. R. Petzold, Consistent

 C      Initial Condition Calculation for Differential-Algebraic

 C      Systems, LLNL Report UCRL-JC-122175, August 1995; submitted to

 C      SIAM J. Sci. Comp.

 C

 C***ROUTINES CALLED

 C

 C   The following are all the subordinate routines used by DDASPK.

 C

 C   DDASIC computes consistent initial conditions.

 C   DYYPNW updates Y and YPRIME in linesearch for initial condition

 C          calculation.

 C   DDSTP  carries out one step of the integration.

 C   DCNSTR/DCNST0 check the current solution for constraint violations.

 C   DDAWTS sets error weight quantities.

 C   DINVWT tests and inverts the error weights.

 C   DDATRP performs interpolation to get an output solution.

 C   DDWNRM computes the weighted root-mean-square norm of a vector.

 C   D1MACH provides the unit roundoff of the computer.

 C   XERRWD/XSETF/XSETUN/IXSAV is a package to handle error messages.

 C   DDASID nonlinear equation driver to initialize Y and YPRIME using

 C          direct linear system solver methods.  Interfaces to Newton

 C          solver (direct case).

 C   DNSID  solves the nonlinear system for unknown initial values by

 C          modified Newton iteration and direct linear system methods.

 C   DLINSD carries out linesearch algorithm for initial condition

 C          calculation (direct case).

 C   DFNRMD calculates weighted norm of preconditioned residual in

 C          initial condition calculation (direct case).

 C   DNEDD  nonlinear equation driver for direct linear system solver

 C          methods.  Interfaces to Newton solver (direct case).

 C   DMATD  assembles the iteration matrix (direct case).

 C   DNSD   solves the associated nonlinear system by modified

 C          Newton iteration and direct linear system methods.

 C   DSLVD  interfaces to linear system solver (direct case).

 C   DDASIK nonlinear equation driver to initialize Y and YPRIME using

 C          Krylov iterative linear system methods.  Interfaces to

 C          Newton solver (Krylov case).

 C   DNSIK  solves the nonlinear system for unknown initial values by

 C          Newton iteration and Krylov iterative linear system methods.

 C   DLINSK carries out linesearch algorithm for initial condition

 C          calculation (Krylov case).

 C   DFNRMK calculates weighted norm of preconditioned residual in

 C          initial condition calculation (Krylov case).

 C   DNEDK  nonlinear equation driver for iterative linear system solver

 C          methods.  Interfaces to Newton solver (Krylov case).

 C   DNSK   solves the associated nonlinear system by Inexact Newton

 C          iteration and (linear) Krylov iteration.

 C   DSLVK  interfaces to linear system solver (Krylov case).

 C   DSPIGM solves a linear system by SPIGMR algorithm.

 C   DATV   computes matrix-vector product in Krylov algorithm.

 C   DORTH  performs orthogonalization of Krylov basis vectors.

 C   DHEQR  performs QR factorization of Hessenberg matrix.

 C   DHELS  finds least-squares solution of Hessenberg linear system.

 C   DGETRF, DGETRS, DGBTRF, DGBTRS are LAPACK routines for solving

 C          linear systems (dense or band direct methods).

 C   DAXPY, DCOPY, DDOT, DNRM2, DSCAL are Basic Linear Algebra (BLAS)

 C          routines.

 C

 C The routines called directly by DDASPK are:

 C   DCNST0, DDAWTS, DINVWT, D1MACH, DDWNRM, DDASIC, DDATRP, DDSTP,

 C   XERRWD

 C

 C***END PROLOGUE DDASPK

 C

 C

       IMPLICIT DOUBLE PRECISION(a-h,o-z)

       LOGICAL DONE, LAVL, LCFN, LCFL, LWARN

       dimension y(*),yprime(*)

       dimension info(20)

       dimension rwork(lrw),iwork(liw)

       dimension rtol(*),atol(*)

       dimension rpar(*),ipar(*)

       CHARACTER MSG*80

       EXTERNAL  res, jac, psol, ddasid, ddasik, dnedd, dnedk

 C

 C     Set pointers into IWORK.

 C

       parameter(lml=1, lmu=2, lmtype=4,

      *   liwm=1, lmxord=3, ljcalc=5, lphase=6, lk=7, lkold=8,

      *   lns=9, lnstl=10, lnst=11, lnre=12, lnje=13, letf=14, lncfn=15,

      *   lncfl=16, lniw=17, lnrw=18, lnni=19, lnli=20, lnps=21,

      *   lnpd=22, lmiter=23, lmaxl=24, lkmp=25, lnrmax=26, llnwp=27,

      *   llniwp=28, llocwp=29, llciwp=30, lkprin=31,

      *   lmxnit=32, lmxnj=33, lmxnh=34, llsoff=35, licns=41)

 C

 C     Set pointers into RWORK.

 C

       parameter(ltstop=1, lhmax=2, lh=3, ltn=4, lcj=5, lcjold=6,

      *   lhold=7, ls=8, lround=9, lepli=10, lsqrn=11, lrsqrn=12,

      *   lepcon=13, lstol=14, lepin=15,

      *   lalpha=21, lbeta=27, lgamma=33, lpsi=39, lsigma=45, ldelta=51)

 C

       SAVE lid, lenid, nonneg

 C

 C

 C***FIRST EXECUTABLE STATEMENT  DDASPK

 C

 C

       IF(info(1).NE.0) GO TO 100

 C

 C-----------------------------------------------------------------------

 C     This block is executed for the initial call only.

 C     It contains checking of inputs and initializations.

 C-----------------------------------------------------------------------

 C

 C     First check INFO array to make sure all elements of INFO

 C     Are within the proper range.  (INFO(1) is checked later, because

 C     it must be tested on every call.) ITEMP holds the location

 C     within INFO which may be out of range.

 C

       DO 10 i=2,9

          itemp = i

          IF (info(i) .NE. 0 .AND. info(i) .NE. 1) GO TO 701

  10      CONTINUE

       itemp = 10

       IF(info(10).LT.0 .OR. info(10).GT.3) GO TO 701

       itemp = 11

       IF(info(11).LT.0 .OR. info(11).GT.2) GO TO 701

       DO 15 i=12,17

          itemp = i

          IF (info(i) .NE. 0 .AND. info(i) .NE. 1) GO TO 701

  15      CONTINUE

       itemp = 18

       IF(info(18).LT.0 .OR. info(18).GT.2) GO TO 701


 C

 C     Check NEQ to see if it is positive.

 C

       IF (neq .LE. 0) GO TO 702

 C

 C     Check and compute maximum order.

 C

       mxord=5

       IF (info(9) .NE. 0) THEN

          mxord=iwork(lmxord)

          IF (mxord .LT. 1 .OR. mxord .GT. 5) GO TO 703

          ENDIF

       iwork(lmxord)=mxord

 C

 C     Set and/or check inputs for constraint checking (INFO(10) .NE. 0).

 C     Set values for ICNFLG, NONNEG, and pointer LID.

 C

       icnflg = 0

       nonneg = 0

       lid = licns

       IF (info(10) .EQ. 0) GO TO 20

       IF (info(10) .EQ. 1) THEN

          icnflg = 1

          nonneg = 0

          lid = licns + neq

       ELSEIF (info(10) .EQ. 2) THEN

          icnflg = 0

          nonneg = 1

       ELSE

          icnflg = 1

          nonneg = 1

          lid = licns + neq

       ENDIF

 C

  20   CONTINUE

 C

 C     Set and/or check inputs for Krylov solver (INFO(12) .NE. 0).

 C     If indicated, set default values for MAXL, KMP, NRMAX, and EPLI.

 C     Otherwise, verify inputs required for iterative solver.

 C

       IF (info(12) .EQ. 0) GO TO 25

 C

       iwork(lmiter) = info(12)

       IF (info(13) .EQ. 0) THEN

          iwork(lmaxl) = min(5,neq)

          iwork(lkmp) = iwork(lmaxl)

          iwork(lnrmax) = 5

          rwork(lepli) = 0.05d0

       ELSE

          IF(iwork(lmaxl) .LT. 1 .OR. iwork(lmaxl) .GT. neq) GO TO 720

          IF(iwork(lkmp) .LT. 1 .OR. iwork(lkmp) .GT. iwork(lmaxl))

      1      GO TO 721

          IF(iwork(lnrmax) .LT. 0) GO TO 722

          IF(rwork(lepli).LE.0.0d0 .OR. rwork(lepli).GE.1.0d0)GO TO 723

          ENDIF

 C

  25   CONTINUE

 C

 C     Set and/or check controls for the initial condition calculation

 C     (INFO(11) .GT. 0).  If indicated, set default values.

 C     Otherwise, verify inputs required for iterative solver.

 C

       IF (info(11) .EQ. 0) GO TO 30

       IF (info(17) .EQ. 0) THEN

         iwork(lmxnit) = 5

         IF (info(12) .GT. 0) iwork(lmxnit) = 15

         iwork(lmxnj) = 6

         IF (info(12) .GT. 0) iwork(lmxnj) = 2

         iwork(lmxnh) = 5

         iwork(llsoff) = 0

         rwork(lepin) = 0.01d0

       ELSE

         IF (iwork(lmxnit) .LE. 0) GO TO 725

         IF (iwork(lmxnj) .LE. 0) GO TO 725

         IF (iwork(lmxnh) .LE. 0) GO TO 725

         lsoff = iwork(llsoff)

         IF (lsoff .LT. 0 .OR. lsoff .GT. 1) GO TO 725

         IF (rwork(lepin) .LE. 0.0d0) GO TO 725

         ENDIF

 C

  30   CONTINUE

 C

 C     Below is the computation and checking of the work array lengths

 C     LENIW and LENRW, using direct methods (INFO(12) = 0) or

 C     the Krylov methods (INFO(12) = 1).

 C

       lenic = 0

       IF (info(10) .EQ. 1 .OR. info(10) .EQ. 3) lenic = neq

       lenid = 0

       IF (info(11) .EQ. 1 .OR. info(16) .EQ. 1) lenid = neq

       IF (info(12) .EQ. 0) THEN

 C

 C        Compute MTYPE, etc.  Check ML and MU.

 C

          ncphi = max(mxord + 1, 4)

          IF(info(6).EQ.0) THEN

             lenpd = neq**2

             lenrw = 50 + (ncphi+3)*neq + lenpd

             IF(info(5).EQ.0) THEN

                iwork(lmtype)=2

             ELSE

                iwork(lmtype)=1

             ENDIF

          ELSE

             IF(iwork(lml).LT.0.OR.iwork(lml).GE.neq)GO TO 717

             IF(iwork(lmu).LT.0.OR.iwork(lmu).GE.neq)GO TO 718

             lenpd=(2*iwork(lml)+iwork(lmu)+1)*neq

             IF(info(5).EQ.0) THEN

                iwork(lmtype)=5

                mband=iwork(lml)+iwork(lmu)+1

                msave=(neq/mband)+1

                lenrw = 50 + (ncphi+3)*neq + lenpd + 2*msave

             ELSE

                iwork(lmtype)=4

                lenrw = 50 + (ncphi+3)*neq + lenpd

             ENDIF

          ENDIF

 C

 C        Compute LENIW, LENWP, LENIWP.

 C

          leniw = 40 + lenic + lenid + neq

          lenwp = 0

          leniwp = 0

 C

       ELSE IF (info(12) .EQ. 1)  THEN

          maxl = iwork(lmaxl)

          lenwp = iwork(llnwp)

          leniwp = iwork(llniwp)

          lenpd = (maxl+3+min0(1,maxl-iwork(lkmp)))*neq

      1         + (maxl+3)*maxl + 1 + lenwp

          lenrw = 50 + (iwork(lmxord)+5)*neq + lenpd

          leniw = 40 + lenic + lenid + leniwp

 C

       ENDIF

       IF(info(16) .NE. 0) lenrw = lenrw + neq

 C

 C     Check lengths of RWORK and IWORK.

 C

       iwork(lniw)=leniw

       iwork(lnrw)=lenrw

       iwork(lnpd)=lenpd

       iwork(llocwp) = lenpd-lenwp+1

       IF(lrw.LT.lenrw)GO TO 704

       IF(liw.LT.leniw)GO TO 705

 C

 C     Check ICNSTR for legality.

 C

       IF (lenic .GT. 0) THEN

         DO 40 i = 1,neq

           ici = iwork(licns-1+i)

           IF (ici .LT. -2 .OR. ici .GT. 2) GO TO 726

  40       CONTINUE

         ENDIF

 C

 C     Check Y for consistency with constraints.

 C

       IF (lenic .GT. 0) THEN

         CALL dcnst0(neq,y,iwork(licns),iret)

         IF (iret .NE. 0) GO TO 727

         ENDIF

 C

 C     Check ID for legality.

 C

       IF (lenid .GT. 0) THEN

         DO 50 i = 1,neq

           idi = iwork(lid-1+i)

           IF (idi .NE. 1 .AND. idi .NE. -1) GO TO 724

  50       CONTINUE

         ENDIF

 C

 C     Check to see that TOUT is different from T.

 C

       IF(tout .EQ. t)GO TO 719

 C

 C     Check HMAX.

 C

       IF(info(7) .NE. 0) THEN

          hmax = rwork(lhmax)

          IF (hmax .LE. 0.0d0) GO TO 710

          ENDIF

 C

 C     Initialize counters and other flags.

 C

       iwork(lnst)=0

       iwork(lnre)=0

       iwork(lnje)=0

       iwork(letf)=0

       iwork(lncfn)=0

       iwork(lnni)=0

       iwork(lnli)=0

       iwork(lnps)=0

       iwork(lncfl)=0

       iwork(lkprin)=info(18)

       idid=1

       GO TO 200

 C

 C-----------------------------------------------------------------------

 C     This block is for continuation calls only.

 C     Here we check INFO(1), and if the last step was interrupted,

 C     we check whether appropriate action was taken.

 C-----------------------------------------------------------------------

 C

 100   CONTINUE

       IF(info(1).EQ.1)GO TO 110

       itemp = 1

       IF(info(1).NE.-1)GO TO 701

 C

 C     If we are here, the last step was interrupted by an error

 C     condition from DDSTP, and appropriate action was not taken.

 C     This is a fatal error.

 C

       msg = 'DASPK--  THE LAST STEP TERMINATED WITH A NEGATIVE'

       CALL xerrwd(msg,49,201,0,0,0,0,0,0.0d0,0.0d0)

       msg = 'DASPK--  VALUE (=I1) OF IDID AND NO APPROPRIATE'

       CALL xerrwd(msg,47,202,0,1,idid,0,0,0.0d0,0.0d0)

       msg = 'DASPK--  ACTION WAS TAKEN. RUN TERMINATED'

       CALL xerrwd(msg,41,203,1,0,0,0,0,0.0d0,0.0d0)

       RETURN

 110   CONTINUE

 C

 C-----------------------------------------------------------------------

 C     This block is executed on all calls.

 C

 C     Counters are saved for later checks of performance.

 C     Then the error tolerance parameters are checked, and the

 C     work array pointers are set.

 C-----------------------------------------------------------------------

 C

 200   CONTINUE

 C

 C     Save counters for use later.

 C

       iwork(lnstl)=iwork(lnst)

       nli0 = iwork(lnli)

       nni0 = iwork(lnni)

       ncfn0 = iwork(lncfn)

       ncfl0 = iwork(lncfl)

       nwarn = 0

 C

 C     Check RTOL and ATOL.

 C

       nzflg = 0

       rtoli = rtol(1)

       atoli = atol(1)

       DO 210 i=1,neq

          IF (info(2) .EQ. 1) rtoli = rtol(i)

          IF (info(2) .EQ. 1) atoli = atol(i)

          IF (rtoli .GT. 0.0d0 .OR. atoli .GT. 0.0d0) nzflg = 1

          IF (rtoli .LT. 0.0d0) GO TO 706

          IF (atoli .LT. 0.0d0) GO TO 707

 210      CONTINUE

       IF (nzflg .EQ. 0) GO TO 708

 C

 C     Set pointers to RWORK and IWORK segments.

 C     For direct methods, SAVR is not used.

 C

       iwork(llciwp) = lid + lenid

       lsavr = ldelta

       IF (info(12) .NE. 0) lsavr = ldelta + neq

       le = lsavr + neq

       lwt = le + neq

       lvt = lwt

       IF (info(16) .NE. 0) lvt = lwt + neq

       lphi = lvt + neq

       lwm = lphi + (iwork(lmxord)+1)*neq

       IF (info(1) .EQ. 1) GO TO 400

 C

 C-----------------------------------------------------------------------

 C     This block is executed on the initial call only.

 C     Set the initial step size, the error weight vector, and PHI.

 C     Compute unknown initial components of Y and YPRIME, if requested.

 C-----------------------------------------------------------------------

 C

 300   CONTINUE

       tn=t

       idid=1

 C

 C     Set error weight array WT and altered weight array VT.

 C

       CALL ddawts(neq,info(2),rtol,atol,y,rwork(lwt),rpar,ipar)

       CALL dinvwt(neq,rwork(lwt),ier)

       IF (ier .NE. 0) GO TO 713

       IF (info(16) .NE. 0) THEN

         DO 305 i = 1, neq

  305      rwork(lvt+i-1) = max(iwork(lid+i-1),0)*rwork(lwt+i-1)

         ENDIF

 C

 C     Compute unit roundoff and HMIN.

 C

       uround = d1mach(4)

       rwork(lround) = uround

       hmin = 4.0d0*uround*max(abs(t),abs(tout))

 C

 C     Set/check STPTOL control for initial condition calculation.

 C

       IF (info(11) .NE. 0) THEN

         IF( info(17) .EQ. 0) THEN

           rwork(lstol) = uround**.6667d0

         ELSE

           IF (rwork(lstol) .LE. 0.0d0) GO TO 725

           ENDIF

         ENDIF

 C

 C     Compute EPCON and square root of NEQ and its reciprocal, used

 C     inside iterative solver.

 C

       rwork(lepcon) = 0.33d0

       floatn = neq

       rwork(lsqrn) = sqrt(floatn)

       rwork(lrsqrn) = 1.d0/rwork(lsqrn)

 C

 C     Check initial interval to see that it is long enough.

 C

       tdist = abs(tout - t)

       IF(tdist .LT. hmin) GO TO 714

 C

 C     Check H0, if this was input.

 C

       IF (info(8) .EQ. 0) GO TO 310

          h0 = rwork(lh)

          IF ((tout - t)*h0 .LT. 0.0d0) GO TO 711

          IF (h0 .EQ. 0.0d0) GO TO 712

          GO TO 320

 310    CONTINUE

 C

 C     Compute initial stepsize, to be used by either

 C     DDSTP or DDASIC, depending on INFO(11).

 C

       h0 = 0.001d0*tdist

       ypnorm = ddwnrm(neq,yprime,rwork(lvt),rpar,ipar)

       IF (ypnorm .GT. 0.5d0/h0) h0 = 0.5d0/ypnorm

       h0 = sign(h0,tout-t)

 C

 C     Adjust H0 if necessary to meet HMAX bound.

 C

 320   IF (info(7) .EQ. 0) GO TO 330

          rh = abs(h0)/rwork(lhmax)

          IF (rh .GT. 1.0d0) h0 = h0/rh

 C

 C     Check against TSTOP, if applicable.

 C

 330   IF (info(4) .EQ. 0) GO TO 340

          tstop = rwork(ltstop)

          IF ((tstop - t)*h0 .LT. 0.0d0) GO TO 715

          IF ((t + h0 - tstop)*h0 .GT. 0.0d0) h0 = tstop - t

          IF ((tstop - tout)*h0 .LT. 0.0d0) GO TO 709

 C

 340   IF (info(11) .EQ. 0) GO TO 370

 C

 C     Compute unknown components of initial Y and YPRIME, depending

 C     on INFO(11) and INFO(12).  INFO(12) represents the nonlinear

 C     solver type (direct/Krylov).  Pass the name of the specific

 C     nonlinear solver, depending on INFO(12).  The location of the work

 C     arrays SAVR, YIC, YPIC, PWK also differ in the two cases.

 C

       nwt = 1

       epconi = rwork(lepin)*rwork(lepcon)

 350   IF (info(12) .EQ. 0) THEN

          lyic = lphi + 2*neq

          lypic = lyic + neq

          lpwk = lypic

          CALL ddasic(tn,y,yprime,neq,info(11),iwork(lid),

      *     res,jac,psol,h0,rwork(lwt),nwt,idid,rpar,ipar,

      *     rwork(lphi),rwork(lsavr),rwork(ldelta),rwork(le),

      *     rwork(lyic),rwork(lypic),rwork(lpwk),rwork(lwm),iwork(liwm),

      *     hmin,rwork(lround),rwork(lepli),rwork(lsqrn),rwork(lrsqrn),

      *     epconi,rwork(lstol),info(15),icnflg,iwork(licns),ddasid)

       ELSE IF (info(12) .EQ. 1) THEN

          lyic = lwm

          lypic = lyic + neq

          lpwk = lypic + neq

          CALL ddasic(tn,y,yprime,neq,info(11),iwork(lid),

      *     res,jac,psol,h0,rwork(lwt),nwt,idid,rpar,ipar,

      *     rwork(lphi),rwork(lsavr),rwork(ldelta),rwork(le),

      *     rwork(lyic),rwork(lypic),rwork(lpwk),rwork(lwm),iwork(liwm),

      *     hmin,rwork(lround),rwork(lepli),rwork(lsqrn),rwork(lrsqrn),

      *     epconi,rwork(lstol),info(15),icnflg,iwork(licns),ddasik)

       ENDIF

 C

       IF (idid .LT. 0) GO TO 600

 C

 C     DDASIC was successful.  If this was the first call to DDASIC,

 C     update the WT array (with the current Y) and call it again.

 C

       IF (nwt .EQ. 2) GO TO 355

       nwt = 2

       CALL ddawts(neq,info(2),rtol,atol,y,rwork(lwt),rpar,ipar)

       CALL dinvwt(neq,rwork(lwt),ier)

       IF (ier .NE. 0) GO TO 713

       GO TO 350

 C

 C     If INFO(14) = 1, return now with IDID = 4.

 C

 355   IF (info(14) .EQ. 1) THEN

         idid = 4

         h = h0

         IF (info(11) .EQ. 1) rwork(lhold) = h0

         GO TO 590

       ENDIF

 C

 C     Update the WT and VT arrays one more time, with the new Y.

 C

       CALL ddawts(neq,info(2),rtol,atol,y,rwork(lwt),rpar,ipar)

       CALL dinvwt(neq,rwork(lwt),ier)

       IF (ier .NE. 0) GO TO 713

       IF (info(16) .NE. 0) THEN

         DO 357 i = 1, neq

  357      rwork(lvt+i-1) = max(iwork(lid+i-1),0)*rwork(lwt+i-1)

         ENDIF

 C

 C     Reset the initial stepsize to be used by DDSTP.

 C     Use H0, if this was input.  Otherwise, recompute H0,

 C     and adjust it if necessary to meet HMAX bound.

 C

       IF (info(8) .NE. 0) THEN

          h0 = rwork(lh)

          GO TO 360

          ENDIF

 C

       h0 = 0.001d0*tdist

       ypnorm = ddwnrm(neq,yprime,rwork(lvt),rpar,ipar)

       IF (ypnorm .GT. 0.5d0/h0) h0 = 0.5d0/ypnorm

       h0 = sign(h0,tout-t)

 C

 360   IF (info(7) .NE. 0) THEN

          rh = abs(h0)/rwork(lhmax)

          IF (rh .GT. 1.0d0) h0 = h0/rh

          ENDIF

 C

 C     Check against TSTOP, if applicable.

 C

       IF (info(4) .NE. 0) THEN

          tstop = rwork(ltstop)

          IF ((t + h0 - tstop)*h0 .GT. 0.0d0) h0 = tstop - t

          ENDIF

 C

 C     Load H and RWORK(LH) with H0.

 C

 370   h = h0

       rwork(lh) = h

 C

 C     Load Y and H*YPRIME into PHI(*,1) and PHI(*,2).

 C

       itemp = lphi + neq

       DO 380 i = 1,neq

          rwork(lphi + i - 1) = y(i)

 380      rwork(itemp + i - 1) = h*yprime(i)

 C

       GO TO 500

 C

 C-----------------------------------------------------------------------

 C     This block is for continuation calls only.

 C     Its purpose is to check stop conditions before taking a step.

 C     Adjust H if necessary to meet HMAX bound.

 C-----------------------------------------------------------------------

 C

 400   CONTINUE

       uround=rwork(lround)

       done = .false.

       tn=rwork(ltn)

       h=rwork(lh)

       IF(info(7) .EQ. 0) GO TO 410

          rh = abs(h)/rwork(lhmax)

          IF(rh .GT. 1.0d0) h = h/rh

 410   CONTINUE

       IF(t .EQ. tout) GO TO 719

       IF((t - tout)*h .GT. 0.0d0) GO TO 711

       IF(info(4) .EQ. 1) GO TO 430

       IF(info(3) .EQ. 1) GO TO 420

       IF((tn-tout)*h.LT.0.0d0)GO TO 490

       CALL ddatrp(tn,tout,y,yprime,neq,iwork(lkold),

      *  rwork(lphi),rwork(lpsi))

       t=tout

       idid = 3

       done = .true.

       GO TO 490

 420   IF((tn-t)*h .LE. 0.0d0) GO TO 490

       IF((tn - tout)*h .GT. 0.0d0) GO TO 425

       CALL ddatrp(tn,tn,y,yprime,neq,iwork(lkold),

      *  rwork(lphi),rwork(lpsi))

       t = tn

       idid = 1

       done = .true.

       GO TO 490

 425   CONTINUE

       CALL ddatrp(tn,tout,y,yprime,neq,iwork(lkold),

      *  rwork(lphi),rwork(lpsi))

       t = tout

       idid = 3

       done = .true.

       GO TO 490

 430   IF(info(3) .EQ. 1) GO TO 440

       tstop=rwork(ltstop)

       IF((tn-tstop)*h.GT.0.0d0) GO TO 715

       IF((tstop-tout)*h.LT.0.0d0)GO TO 709

       IF((tn-tout)*h.LT.0.0d0)GO TO 450

       CALL ddatrp(tn,tout,y,yprime,neq,iwork(lkold),

      *   rwork(lphi),rwork(lpsi))

       t=tout

       idid = 3

       done = .true.

       GO TO 490

 440   tstop = rwork(ltstop)

       IF((tn-tstop)*h .GT. 0.0d0) GO TO 715

       IF((tstop-tout)*h .LT. 0.0d0) GO TO 709

       IF((tn-t)*h .LE. 0.0d0) GO TO 450

       IF((tn - tout)*h .GT. 0.0d0) GO TO 445

       CALL ddatrp(tn,tn,y,yprime,neq,iwork(lkold),

      *  rwork(lphi),rwork(lpsi))

       t = tn

       idid = 1

       done = .true.

       GO TO 490

 445   CONTINUE

       CALL ddatrp(tn,tout,y,yprime,neq,iwork(lkold),

      *  rwork(lphi),rwork(lpsi))

       t = tout

       idid = 3

       done = .true.

       GO TO 490

 450   CONTINUE

 C

 C     Check whether we are within roundoff of TSTOP.

 C

       IF(abs(tn-tstop).GT.100.0d0*uround*

      *   (abs(tn)+abs(h)))GO TO 460

       CALL ddatrp(tn,tstop,y,yprime,neq,iwork(lkold),

      *  rwork(lphi),rwork(lpsi))

       idid=2

       t=tstop

       done = .true.

       GO TO 490

 460   tnext=tn+h

       IF((tnext-tstop)*h.LE.0.0d0)GO TO 490

       h=tstop-tn

       rwork(lh)=h

 C

 490   IF (done) GO TO 590

 C

 C-----------------------------------------------------------------------

 C     The next block contains the call to the one-step integrator DDSTP.

 C     This is a looping point for the integration steps.

 C     Check for too many steps.

 C     Check for poor Newton/Krylov performance.

 C     Update WT.  Check for too much accuracy requested.

 C     Compute minimum stepsize.

 C-----------------------------------------------------------------------

 C

 500   CONTINUE

 C

 C     Check for too many steps.

 C

       IF((iwork(lnst)-iwork(lnstl)).LT.500) GO TO 505

            idid=-1

            GO TO 527

 C

 C Check for poor Newton/Krylov performance.

 C

 505   IF (info(12) .EQ. 0) GO TO 510

       nstd = iwork(lnst) - iwork(lnstl)

       nnid = iwork(lnni) - nni0

       IF (nstd .LT. 10 .OR. nnid .EQ. 0) GO TO 510

       avlin = real(iwork(lnli) - nli0)/real(nnid)

       rcfn = real(iwork(lncfn) - ncfn0)/real(nstd)

       rcfl = real(iwork(lncfl) - ncfl0)/real(nnid)

       fmaxl = iwork(lmaxl)

       lavl = avlin .GT. fmaxl

       lcfn = rcfn .GT. 0.9d0

       lcfl = rcfl .GT. 0.9d0

       lwarn = lavl .OR. lcfn .OR. lcfl

       IF (.NOT.lwarn) GO TO 510

       nwarn = nwarn + 1

       IF (nwarn .GT. 10) GO TO 510

       IF (lavl) THEN

         msg = 'DASPK-- Warning. Poor iterative algorithm performance   '

         CALL xerrwd (msg, 56, 501, 0, 0, 0, 0, 0, 0.0d0, 0.0d0)

         msg = '      at T = R1. Average no. of linear iterations = R2  '

         CALL xerrwd (msg, 56, 501, 0, 0, 0, 0, 2, tn, avlin)

         ENDIF

       IF (lcfn) THEN

         msg = 'DASPK-- Warning. Poor iterative algorithm performance   '

         CALL xerrwd (msg, 56, 502, 0, 0, 0, 0, 0, 0.0d0, 0.0d0)

         msg = '      at T = R1. Nonlinear convergence failure rate = R2'

         CALL xerrwd (msg, 56, 502, 0, 0, 0, 0, 2, tn, rcfn)

         ENDIF

       IF (lcfl) THEN

         msg = 'DASPK-- Warning. Poor iterative algorithm performance   '

         CALL xerrwd (msg, 56, 503, 0, 0, 0, 0, 0, 0.0d0, 0.0d0)

         msg = '      at T = R1. Linear convergence failure rate = R2   '

         CALL xerrwd (msg, 56, 503, 0, 0, 0, 0, 2, tn, rcfl)

         ENDIF

 C

 C     Update WT and VT, if this is not the first call.

 C

 510   CALL ddawts(neq,info(2),rtol,atol,rwork(lphi),rwork(lwt),

      *            rpar,ipar)

       CALL dinvwt(neq,rwork(lwt),ier)

       IF (ier .NE. 0) THEN

         idid = -3

         GO TO 527

         ENDIF

       IF (info(16) .NE. 0) THEN

         DO 515 i = 1, neq

  515      rwork(lvt+i-1) = max(iwork(lid+i-1),0)*rwork(lwt+i-1)

         ENDIF

 C

 C     Test for too much accuracy requested.

 C

       r = ddwnrm(neq,rwork(lphi),rwork(lwt),rpar,ipar)*100.0d0*uround

       IF (r .LE. 1.0d0) GO TO 525

 C

 C     Multiply RTOL and ATOL by R and return.

 C

       IF(info(2).EQ.1)GO TO 523

            rtol(1)=r*rtol(1)

            atol(1)=r*atol(1)

            idid=-2

            GO TO 527

 523   DO 524 i=1,neq

            rtol(i)=r*rtol(i)

 524        atol(i)=r*atol(i)

       idid=-2

       GO TO 527

 525   CONTINUE

 C

 C     Compute minimum stepsize.

 C

       hmin=4.0d0*uround*max(abs(tn),abs(tout))

 C

 C     Test H vs. HMAX

       IF (info(7) .NE. 0) THEN

          rh = abs(h)/rwork(lhmax)

          IF (rh .GT. 1.0d0) h = h/rh

          ENDIF

 C

 C     Call the one-step integrator.

 C     Note that INFO(12) represents the nonlinear solver type.

 C     Pass the required nonlinear solver, depending upon INFO(12).

 C

       IF (info(12) .EQ. 0) THEN

          CALL ddstp(tn,y,yprime,neq,

      *      res,jac,psol,h,rwork(lwt),rwork(lvt),info(1),idid,rpar,ipar,

      *      rwork(lphi),rwork(lsavr),rwork(ldelta),rwork(le),

      *      rwork(lwm),iwork(liwm),

      *      rwork(lalpha),rwork(lbeta),rwork(lgamma),

      *      rwork(lpsi),rwork(lsigma),

      *      rwork(lcj),rwork(lcjold),rwork(lhold),rwork(ls),hmin,

      *      rwork(lround), rwork(lepli),rwork(lsqrn),rwork(lrsqrn),

      *      rwork(lepcon), iwork(lphase),iwork(ljcalc),info(15),

      *      iwork(lk), iwork(lkold),iwork(lns),nonneg,info(12),

      *      dnedd)

       ELSE IF (info(12) .EQ. 1) THEN

          CALL ddstp(tn,y,yprime,neq,

      *      res,jac,psol,h,rwork(lwt),rwork(lvt),info(1),idid,rpar,ipar,

      *      rwork(lphi),rwork(lsavr),rwork(ldelta),rwork(le),

      *      rwork(lwm),iwork(liwm),

      *      rwork(lalpha),rwork(lbeta),rwork(lgamma),

      *      rwork(lpsi),rwork(lsigma),

      *      rwork(lcj),rwork(lcjold),rwork(lhold),rwork(ls),hmin,

      *      rwork(lround), rwork(lepli),rwork(lsqrn),rwork(lrsqrn),

      *      rwork(lepcon), iwork(lphase),iwork(ljcalc),info(15),

      *      iwork(lk), iwork(lkold),iwork(lns),nonneg,info(12),

      *      dnedk)

       ENDIF

 C

 527   IF(idid.LT.0)GO TO 600

 C

 C-----------------------------------------------------------------------

 C     This block handles the case of a successful return from DDSTP

 C     (IDID=1).  Test for stop conditions.

 C-----------------------------------------------------------------------

 C

       IF(info(4).NE.0)GO TO 540

            IF(info(3).NE.0)GO TO 530

              IF((tn-tout)*h.LT.0.0d0)GO TO 500

              CALL ddatrp(tn,tout,y,yprime,neq,

      *         iwork(lkold),rwork(lphi),rwork(lpsi))

              idid=3

              t=tout

              GO TO 580

 530          IF((tn-tout)*h.GE.0.0d0)GO TO 535

              t=tn

              idid=1

              GO TO 580

 535          CALL ddatrp(tn,tout,y,yprime,neq,

      *         iwork(lkold),rwork(lphi),rwork(lpsi))

              idid=3

              t=tout

              GO TO 580

 540   IF(info(3).NE.0)GO TO 550

       IF((tn-tout)*h.LT.0.0d0)GO TO 542

          CALL ddatrp(tn,tout,y,yprime,neq,

      *     iwork(lkold),rwork(lphi),rwork(lpsi))

          t=tout

          idid=3

          GO TO 580

 542   IF(abs(tn-tstop).LE.100.0d0*uround*

      *   (abs(tn)+abs(h)))GO TO 545

       tnext=tn+h

       IF((tnext-tstop)*h.LE.0.0d0)GO TO 500

       h=tstop-tn

       GO TO 500

 545   CALL ddatrp(tn,tstop,y,yprime,neq,

      *  iwork(lkold),rwork(lphi),rwork(lpsi))

       idid=2

       t=tstop

       GO TO 580

 550   IF((tn-tout)*h.GE.0.0d0)GO TO 555

       IF(abs(tn-tstop).LE.100.0d0*uround*(abs(tn)+abs(h)))GO TO 552

       t=tn

       idid=1

       GO TO 580

 552   CALL ddatrp(tn,tstop,y,yprime,neq,

      *  iwork(lkold),rwork(lphi),rwork(lpsi))

       idid=2

       t=tstop

       GO TO 580

 555   CALL ddatrp(tn,tout,y,yprime,neq,

      *   iwork(lkold),rwork(lphi),rwork(lpsi))

       t=tout

       idid=3

 580   CONTINUE

 C

 C-----------------------------------------------------------------------

 C     All successful returns from DDASPK are made from this block.

 C-----------------------------------------------------------------------

 C

 590   CONTINUE

       rwork(ltn)=tn

       rwork(lh)=h

       RETURN

 C

 C-----------------------------------------------------------------------

 C     This block handles all unsuccessful returns other than for

 C     illegal input.

 C-----------------------------------------------------------------------

 C

 600   CONTINUE

       itemp = -idid

       GO TO (610,620,630,700,655,640,650,660,670,675,

      *  680,685,690,695), itemp

 C

 C     The maximum number of steps was taken before

 C     reaching tout.

 C

 610   msg = 'DASPK--  AT CURRENT T (=R1)  500 STEPS'

       CALL xerrwd(msg,38,610,0,0,0,0,1,tn,0.0d0)

       msg = 'DASPK--  TAKEN ON THIS CALL BEFORE REACHING TOUT'

       CALL xerrwd(msg,48,611,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Too much accuracy for machine precision.

 C

 620   msg = 'DASPK--  AT T (=R1) TOO MUCH ACCURACY REQUESTED'

       CALL xerrwd(msg,47,620,0,0,0,0,1,tn,0.0d0)

       msg = 'DASPK--  FOR PRECISION OF MACHINE. RTOL AND ATOL'

       CALL xerrwd(msg,48,621,0,0,0,0,0,0.0d0,0.0d0)

       msg = 'DASPK--  WERE INCREASED TO APPROPRIATE VALUES'

       CALL xerrwd(msg,45,622,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     WT(I) .LE. 0.0D0 for some I (not at start of problem).

 C

 630   msg = 'DASPK--  AT T (=R1) SOME ELEMENT OF WT'

       CALL xerrwd(msg,38,630,0,0,0,0,1,tn,0.0d0)

       msg = .LE.'DASPK--  HAS BECOME  0.0'

       CALL xerrwd(msg,28,631,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Error test failed repeatedly or with H=HMIN.

 C

 640   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,640,0,0,0,0,2,tn,h)

       msg='DASPK--  ERROR TEST FAILED REPEATEDLY OR WITH ABS(H)=HMIN'

       CALL xerrwd(msg,57,641,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Nonlinear solver failed to converge repeatedly or with H=HMIN.

 C

 650   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,650,0,0,0,0,2,tn,h)

       msg = 'DASPK--  NONLINEAR SOLVER FAILED TO CONVERGE'

       CALL xerrwd(msg,44,651,0,0,0,0,0,0.0d0,0.0d0)

       msg = 'DASPK--  REPEATEDLY OR WITH ABS(H)=HMIN'

       CALL xerrwd(msg,40,652,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     The preconditioner had repeated failures.

 C

 655   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,655,0,0,0,0,2,tn,h)

       msg = 'DASPK--  PRECONDITIONER HAD REPEATED FAILURES.'

       CALL xerrwd(msg,46,656,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     The iteration matrix is singular.

 C

 660   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,660,0,0,0,0,2,tn,h)

       msg = 'DASPK--  ITERATION MATRIX IS SINGULAR.'

       CALL xerrwd(msg,38,661,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Nonlinear system failure preceded by error test failures.

 C

 670   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,670,0,0,0,0,2,tn,h)

       msg = 'DASPK--  NONLINEAR SOLVER COULD NOT CONVERGE.'

       CALL xerrwd(msg,45,671,0,0,0,0,0,0.0d0,0.0d0)

       msg = 'DASPK--  ALSO, THE ERROR TEST FAILED REPEATEDLY.'

       CALL xerrwd(msg,49,672,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Nonlinear system failure because IRES = -1.

 C

 675   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,675,0,0,0,0,2,tn,h)

       msg = 'DASPK--  NONLINEAR SYSTEM SOLVER COULD NOT CONVERGE'

       CALL xerrwd(msg,51,676,0,0,0,0,0,0.0d0,0.0d0)

       msg = 'DASPK--  BECAUSE IRES WAS EQUAL TO MINUS ONE'

       CALL xerrwd(msg,44,677,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Failure because IRES = -2.

 C

 680   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2)'

       CALL xerrwd(msg,40,680,0,0,0,0,2,tn,h)

       msg = 'DASPK--  IRES WAS EQUAL TO MINUS TWO'

       CALL xerrwd(msg,36,681,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Failed to compute initial YPRIME.

 C

 685   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,685,0,0,0,0,0,0.0d0,0.0d0)

       msg = 'DASPK--  INITIAL (Y,YPRIME) COULD NOT BE COMPUTED'

       CALL xerrwd(msg,49,686,0,0,0,0,2,tn,h0)

       GO TO 700

 C

 C     Failure because IER was negative from PSOL.

 C

 690   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2)'

       CALL xerrwd(msg,40,690,0,0,0,0,2,tn,h)

       msg = 'DASPK--  IER WAS NEGATIVE FROM PSOL'

       CALL xerrwd(msg,35,691,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C     Failure because the linear system solver could not converge.

 C

 695   msg = 'DASPK--  AT T (=R1) AND STEPSIZE H (=R2) THE'

       CALL xerrwd(msg,44,695,0,0,0,0,2,tn,h)

       msg = 'DASPK--  LINEAR SYSTEM SOLVER COULD NOT CONVERGE.'

       CALL xerrwd(msg,50,696,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 700

 C

 C

 700   CONTINUE

       info(1)=-1

       t=tn

       rwork(ltn)=tn

       rwork(lh)=h

       RETURN

 C

 C-----------------------------------------------------------------------

 C     This block handles all error returns due to illegal input,

 C     as detected before calling DDSTP.

 C     First the error message routine is called.  If this happens

 C     twice in succession, execution is terminated.

 C-----------------------------------------------------------------------

 C

 701   msg = 'DASPK--  ELEMENT (=I1) OF INFO VECTOR IS NOT VALID'

       CALL xerrwd(msg,50,1,0,1,itemp,0,0,0.0d0,0.0d0)

       GO TO 750

 702   msg = .LE.'DASPK--  NEQ (=I1)  0'

       CALL xerrwd(msg,25,2,0,1,neq,0,0,0.0d0,0.0d0)

       GO TO 750

 703   msg = 'DASPK--  MAXORD (=I1) NOT IN RANGE'

       CALL xerrwd(msg,34,3,0,1,mxord,0,0,0.0d0,0.0d0)

       GO TO 750

 704   msg='DASPK--  RWORK LENGTH NEEDED, LENRW (=I1), EXCEEDS LRW (=I2)'

       CALL xerrwd(msg,60,4,0,2,lenrw,lrw,0,0.0d0,0.0d0)

       GO TO 750

 705   msg='DASPK--  IWORK LENGTH NEEDED, LENIW (=I1), EXCEEDS LIW (=I2)'

       CALL xerrwd(msg,60,5,0,2,leniw,liw,0,0.0d0,0.0d0)

       GO TO 750

 706   msg = .LT.'DASPK--  SOME ELEMENT OF RTOL IS  0'

       CALL xerrwd(msg,39,6,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 707   msg = .LT.'DASPK--  SOME ELEMENT OF ATOL IS  0'

       CALL xerrwd(msg,39,7,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 708   msg = 'DASPK--  ALL ELEMENTS OF RTOL AND ATOL ARE ZERO'

       CALL xerrwd(msg,47,8,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 709   msg='DASPK--  INFO(4) = 1 AND TSTOP (=R1) BEHIND TOUT (=R2)'

       CALL xerrwd(msg,54,9,0,0,0,0,2,tstop,tout)

       GO TO 750

 710   msg = .LT.'DASPK--  HMAX (=R1)  0.0'

       CALL xerrwd(msg,28,10,0,0,0,0,1,hmax,0.0d0)

       GO TO 750

 711   msg = 'DASPK--  TOUT (=R1) BEHIND T (=R2)'

       CALL xerrwd(msg,34,11,0,0,0,0,2,tout,t)

       GO TO 750

 712   msg = 'DASPK--  INFO(8)=1 AND H0=0.0'

       CALL xerrwd(msg,29,12,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 713   msg = .LE.'DASPK--  SOME ELEMENT OF WT IS  0.0'

       CALL xerrwd(msg,39,13,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 714   msg='DASPK-- TOUT (=R1) TOO CLOSE TO T (=R2) TO START INTEGRATION'

       CALL xerrwd(msg,60,14,0,0,0,0,2,tout,t)

       GO TO 750

 715   msg = 'DASPK--  INFO(4)=1 AND TSTOP (=R1) BEHIND T (=R2)'

       CALL xerrwd(msg,49,15,0,0,0,0,2,tstop,t)

       GO TO 750

 717   msg = .LT..GT.'DASPK--  ML (=I1) ILLEGAL. EITHER  0 OR  NEQ'

       CALL xerrwd(msg,52,17,0,1,iwork(lml),0,0,0.0d0,0.0d0)

       GO TO 750

 718   msg = .LT..GT.'DASPK--  MU (=I1) ILLEGAL. EITHER  0 OR  NEQ'

       CALL xerrwd(msg,52,18,0,1,iwork(lmu),0,0,0.0d0,0.0d0)

       GO TO 750

 719   msg = 'DASPK--  TOUT (=R1) IS EQUAL TO T (=R2)'

       CALL xerrwd(msg,39,19,0,0,0,0,2,tout,t)

       GO TO 750

 720   msg = .LT..GT.'DASPK--  MAXL (=I1) ILLEGAL. EITHER  1 OR  NEQ'

       CALL xerrwd(msg,54,20,0,1,iwork(lmaxl),0,0,0.0d0,0.0d0)

       GO TO 750

 721   msg = .LT..GT.'DASPK--  KMP (=I1) ILLEGAL. EITHER  1 OR  MAXL'

       CALL xerrwd(msg,54,21,0,1,iwork(lkmp),0,0,0.0d0,0.0d0)

       GO TO 750

 722   msg = .LT.'DASPK--  NRMAX (=I1) ILLEGAL.  0'

       CALL xerrwd(msg,36,22,0,1,iwork(lnrmax),0,0,0.0d0,0.0d0)

       GO TO 750

 723   msg = .LE..GE.'DASPK--  EPLI (=R1) ILLEGAL. EITHER  0.D0 OR  1.D0'

       CALL xerrwd(msg,58,23,0,0,0,0,1,rwork(lepli),0.0d0)

       GO TO 750

 724   msg = .NE.'DASPK--  ILLEGAL IWORK VALUE FOR INFO(11)  0'

       CALL xerrwd(msg,48,24,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 725   msg = 'DASPK--  ONE OF THE INPUTS FOR INFO(17) = 1 IS ILLEGAL'

       CALL xerrwd(msg,54,25,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 726   msg = .NE.'DASPK--  ILLEGAL IWORK VALUE FOR INFO(10)  0'

       CALL xerrwd(msg,48,26,0,0,0,0,0,0.0d0,0.0d0)

       GO TO 750

 727   msg = 'DASPK--  Y(I) AND IWORK(40+I) (I=I1) INCONSISTENT'

       CALL xerrwd(msg,49,27,0,1,iret,0,0,0.0d0,0.0d0)

       GO TO 750

 750   IF(info(1).EQ.-1) GO TO 760

       info(1)=-1

       idid=-33

       RETURN

 760   msg = 'DASPK--  REPEATED OCCURRENCES OF ILLEGAL INPUT'

       CALL xerrwd(msg,46,701,0,0,0,0,0,0.0d0,0.0d0)

 770   msg = 'DASPK--  RUN TERMINATED. APPARENT INFINITE LOOP'

       CALL xerrwd(msg,47,702,1,0,0,0,0,0.0d0,0.0d0)

       RETURN

 C

 C------END OF SUBROUTINE DDASPK-----------------------------------------

       END

max
charNDArray max(char d, const charNDArray &m)
Definition: chNDArray.cc:230

min
charNDArray min(char d, const charNDArray &m)
Definition: chNDArray.cc:207

d1mach
double precision function d1mach(i)
Definition: d1mach.f:23

real
ColumnVector real(const ComplexColumnVector &a)
Definition: dColVector.cc:137

dcnst0
subroutine dcnst0(NEQ, Y, ICNSTR, IRET)
Definition: dcnst0.f:6

ddasic
subroutine ddasic(X, Y, YPRIME, NEQ, ICOPT, ID, RES, JAC, PSOL, H, WT, NIC, IDID, RPAR, IPAR, PHI, SAVR, DELTA, E, YIC, YPIC, PWK, WM, IWM, HMIN, UROUND, EPLI, SQRTN, RSQRTN, EPCONI, STPTOL, JFLG, ICNFLG, ICNSTR, NLSIC)
Definition: ddasic.f:9

ddasid
subroutine ddasid(X, Y, YPRIME, NEQ, ICOPT, ID, RES, JACD, PDUM, H, WT, JSDUM, RPAR, IPAR, DUMSVR, DELTA, R, YIC, YPIC, DUMPWK, WM, IWM, CJ, UROUND, DUME, DUMS, DUMR, EPCON, RATEMX, STPTOL, JFDUM, ICNFLG, ICNSTR, IERNLS)
Definition: ddasid.f:9

ddasik
subroutine ddasik(X, Y, YPRIME, NEQ, ICOPT, ID, RES, JACK, PSOL, H, WT, JSKIP, RPAR, IPAR, SAVR, DELTA, R, YIC, YPIC, PWK, WM, IWM, CJ, UROUND, EPLI, SQRTN, RSQRTN, EPCON, RATEMX, STPTOL, JFLG, ICNFLG, ICNSTR, IERNLS)
Definition: ddasik.f:9

ddaspk
subroutine ddaspk(RES, NEQ, T, Y, YPRIME, TOUT, INFO, RTOL, ATOL, IDID, RWORK, LRW, IWORK, LIW, RPAR, IPAR, JAC, PSOL)
Definition: ddaspk.f:7

ddatrp
subroutine ddatrp(X, XOUT, YOUT, YPOUT, NEQ, KOLD, PHI, PSI)
Definition: ddatrp.f:2

ddawts
subroutine ddawts(NEQ, IWT, RTOL, ATOL, Y, WT, RPAR, IPAR)
Definition: ddawts.f:2

ddstp
subroutine ddstp(X, Y, YPRIME, NEQ, RES, JAC, PSOL, H, WT, VT, JSTART, IDID, RPAR, IPAR, PHI, SAVR, DELTA, E, WM, IWM, ALPHA, BETA, GAMMA, PSI, SIGMA, CJ, CJOLD, HOLD, S, HMIN, UROUND, EPLI, SQRTN, RSQRTN, EPCON, IPHASE, JCALC, JFLG, K, KOLD, NS, NONNEG, NTYPE, NLS)
Definition: ddstp.f:10

ddwnrm
double precision function ddwnrm(NEQ, V, RWT, RPAR, IPAR)
Definition: ddwnrm.f:6

dinvwt
subroutine dinvwt(NEQ, WT, IER)
Definition: dinvwt.f:6

dnedd
subroutine dnedd(X, Y, YPRIME, NEQ, RES, JACD, PDUM, H, WT, JSTART, IDID, RPAR, IPAR, PHI, GAMMA, DUMSVR, DELTA, E, WM, IWM, CJ, CJOLD, CJLAST, S, UROUND, DUME, DUMS, DUMR, EPCON, JCALC, JFDUM, KP1, NONNEG, NTYPE, IERNLS)
Definition: dnedd.f:9

dnedk
subroutine dnedk(X, Y, YPRIME, NEQ, RES, JACK, PSOL, H, WT, JSTART, IDID, RPAR, IPAR, PHI, GAMMA, SAVR, DELTA, E, WM, IWM, CJ, CJOLD, CJLAST, S, UROUND, EPLI, SQRTN, RSQRTN, EPCON, JCALC, JFLG, KP1, NONNEG, NTYPE, IERNLS)
Definition: dnedk.f:9

lgamma
double lgamma(double x)
Definition: lo-specfun.h:336

xerrwd
subroutine xerrwd(MSG, NMES, NERR, LEVEL, NI, I1, I2, NR, R1, R2)
Definition: xerrwd.f:4