crsf2csf.f

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       subroutine crsf2csf(n,t,u,c,s)
       integer n
       complex t(n,n),u(n,n)
       real c(n-1),s(n-1)
       real x,y,z
       integer j
       do j = 1,n-1
          c(j) = 1
       end do
       j = 1
       do while (j < n)
c apply previous rotations to rows
         call crcrot1(j,t(1,j),c,s)
 
         y = t(j+1,j)
         if (y /= 0) then
c 2x2 block, form Givens rotation [c, i*s; i*s, c]
           z = t(j,j+1)
           c(j) = sqrt(z/(z-y))
           s(j) = sqrt(y/(y-z))
c apply new rotation to t(j:j+1,j)
           call crcrot1(2,t(j,j),c(j),s(j))
c apply all rotations to t(1:j+1,j+1)
           call crcrot1(j+1,t(1,j+1),c,s)
c apply new rotation to columns j,j+1
           call crcrot2(j+1,t(1,j),t(1,j+1),c(j),s(j))
c zero subdiagonal entry, skip next row
           t(j+1,j) = 0
           j = j + 2
         else
           j = j + 1
         end if
       end do
 
c apply rotations to last column if needed
       if (j == n) then
         call crcrot1(j,t(1,j),c,s)
       end if
 
c apply stored rotations to all columns of u
       do j = 1,n-1
         if (c(j) /= 1) then
           call crcrot2(n,u(1,j),u(1,j+1),c(j),s(j))
         end if
       end do
 
       end subroutine
 
       subroutine crcrot1(n,x,c,s)
c apply rotations to a column from the left
       integer n
       complex x(n), t
       real c(n-1),s(n-1)
       integer i
       do i = 1,n-1
         if (c(i) /= 1) then
           t = x(i)*c(i) - x(i+1)*cmplx(0,s(i))
           x(i+1) = x(i+1)*c(i) - x(i)*cmplx(0,s(i))
           x(i) = t
         endif
       end do
       end subroutine
 
       subroutine crcrot2(n,x,y,c,s)
c apply a single rotation from the right to a pair of columns
       integer n
       complex x(n),y(n),t
       real c, s
       integer i
       do i = 1,n
         t = x(i)*c + y(i)*cmplx(0,s)
         y(i) = y(i)*c + x(i)*cmplx(0,s)
         x(i) = t
       end do
       end subroutine