Program f07csfe
! F07CSF Example Program Text
! Mark 30.3 Release. nAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: nag_wp, x04dbf, zgttrf, zgttrs
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, ifail, info, ldb, n, nrhs
! .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: b(:,:), d(:), dl(:), du(:), du2(:)
Integer, Allocatable :: ipiv(:)
Character (1) :: clabs(1), rlabs(1)
! .. Executable Statements ..
Write (nout,*) 'F07CSF Example Program Results'
Write (nout,*)
Flush (nout)
! Skip heading in data file
Read (nin,*)
Read (nin,*) n, nrhs
ldb = n
Allocate (b(ldb,nrhs),d(n),dl(n-1),du(n-1),du2(n-2),ipiv(n))
! Read the tridiagonal matrix A from data file
Read (nin,*) du(1:n-1)
Read (nin,*) d(1:n)
Read (nin,*) dl(1:n-1)
! Read the right hand matrix B
Read (nin,*)(b(i,1:nrhs),i=1,n)
! Factorize the tridiagonal matrix A
! The NAG name equivalent of zgttrf is f07crf
Call zgttrf(n,dl,d,du,du2,ipiv,info)
If (info==0) Then
! Solve the equations AX = B
! The NAG name equivalent of zgttrs is f07csf
Call zgttrs('No transpose',n,nrhs,dl,d,du,du2,ipiv,b,ldb,info)
! Print the solution
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04dbf('General',' ',n,nrhs,b,ldb,'Bracketed','F7.4', &
'Solution(s)','Integer',rlabs,'Integer',clabs,80,0,ifail)
Else
Write (nout,99999) 'The (', info, ',', info, ')', &
' element of the factor U is zero'
End If
99999 Format (1X,A,I3,A,I3,A,A)
End Program f07csfe