dlgams.f

Go to the documentation of this file.

*DECK DLGAMS
      SUBROUTINE dlgams (X, DLGAM, SGNGAM)
C***BEGIN PROLOGUE  DLGAMS
C***PURPOSE  Compute the logarithm of the absolute value of the Gamma
C            function.
C***LIBRARY   SLATEC (FNLIB)
C***CATEGORY  C7A
C***TYPE      DOUBLE PRECISION (ALGAMS-S, DLGAMS-D)
C***KEYWORDS  ABSOLUTE VALUE OF THE LOGARITHM OF THE GAMMA FUNCTION,
C             FNLIB, SPECIAL FUNCTIONS
C***AUTHOR  Fullerton, W., (LANL)
C***DESCRIPTION
C
C DLGAMS(X,DLGAM,SGNGAM) calculates the double precision natural
C logarithm of the absolute value of the Gamma function for
C double precision argument X and stores the result in double
C precision argument DLGAM.
C
C***REFERENCES  (NONE)
C***ROUTINES CALLED  DLNGAM
C***REVISION HISTORY  (YYMMDD)
C   770701  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   890531  REVISION DATE from Version 3.2
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C***END PROLOGUE  DLGAMS
      DOUBLE PRECISION x, dlgam, sgngam, dlngam
C***FIRST EXECUTABLE STATEMENT  DLGAMS
      dlgam = dlngam(x)
      sgngam = 1.0d0
      IF (x.GT.0.d0) RETURN
C
      int = mod(-aint(x), 2.0d0) + 0.1d0
      IF (int.EQ.0) sgngam = -1.0d0
C
      RETURN
      END