Program f11drfe
! F11DRF Example Program Text
! Mark 25 Release. NAG Copyright 2014.
! .. Use Statements ..
Use nag_library, Only: f11brf, f11bsf, f11btf, f11drf, f11xnf, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=nag_wp) :: anorm, omega, sigmax, stplhs, &
stprhs, tol
Integer :: i, ifail, ifail1, irevcm, iterm, &
itn, liwork, lwneed, lwork, m, &
maxitn, monit, n, nnz
Character (1) :: ckdrf, ckxnf, norm, precon, trans, &
weight
Character (8) :: method
! .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: a(:), b(:), rdiag(:), work(:), x(:)
Real (Kind=nag_wp), Allocatable :: wgt(:)
Integer, Allocatable :: icol(:), irow(:), iwork(:)
! .. Intrinsic Procedures ..
Intrinsic :: max
! .. Executable Statements ..
Write (nout,*) 'F11DRF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
! Read algorithmic parameters
Read (nin,*) n, m
Read (nin,*) nnz
lwork = max(121+n*(3+m)+m*(m+5),120+7*n,120+(2*n+m)*(m+2)+2*n,120+10*n)
liwork = 2*n + 1
Allocate (a(nnz),b(n),rdiag(n),work(lwork),x(n),wgt(n),icol(nnz), &
irow(nnz),iwork(liwork))
Read (nin,*) method
Read (nin,*) precon, norm, iterm
Read (nin,*) tol, maxitn
Read (nin,*) anorm, sigmax
Read (nin,*) omega
! Read the matrix A
Do i = 1, nnz
Read (nin,*) a(i), irow(i), icol(i)
End Do
! Read rhs vector b and initial approximate solution x
Read (nin,*) b(1:n)
Read (nin,*) x(1:n)
! Call F11BRF to initialize solver
weight = 'N'
monit = 0
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call f11brf(method,precon,norm,weight,iterm,n,m,tol,maxitn,anorm,sigmax, &
monit,lwneed,work,lwork,ifail)
! Calculate reciprocal diagonal matrix elements if necessary
If (precon=='P' .Or. precon=='p') Then
iwork(1:n) = 0
Do i = 1, nnz
If (irow(i)==icol(i)) Then
iwork(irow(i)) = iwork(irow(i)) + 1
If (a(i)/=(0.0E0_nag_wp,0.0E0_nag_wp)) Then
rdiag(irow(i)) = (1.0E0_nag_wp,0.0E0_nag_wp)/a(i)
Else
Write (nout,*) 'Matrix has a zero diagonal element'
Go To 100
End If
End If
End Do
Do i = 1, n
If (iwork(i)==0) Then
Write (nout,*) 'Matrix has a missing diagonal element'
Go To 100
End If
If (iwork(i)>=2) Then
Write (nout,*) 'Matrix has a multiple diagonal element'
Go To 100
End If
End Do
End If
! Call F11BSF to solve the linear system
irevcm = 0
ckxnf = 'C'
ckdrf = 'C'
ifail = 1
loop: Do
Call f11bsf(irevcm,x,b,wgt,work,lwork,ifail)
If (irevcm/=4) Then
ifail1 = 1
Select Case (irevcm)
Case (1)
! Compute matrix-vector product
trans = 'N'
Call f11xnf(trans,n,nnz,a,irow,icol,ckxnf,x,b,ifail1)
ckxnf = 'N'
Case (-1)
! Compute conjugate transposed matrix-vector product
trans = 'T'
Call f11xnf(trans,n,nnz,a,irow,icol,ckxnf,x,b,ifail1)
ckxnf = 'N'
Case (2)
! SSOR preconditioning
trans = 'N'
Call f11drf(trans,n,nnz,a,irow,icol,rdiag,omega,ckdrf,x,b,iwork, &
ifail1)
ckdrf = 'N'
End Select
If (ifail1/=0) irevcm = 6
Else If (ifail==0) Then
! Termination
ifail = 0
Call f11btf(itn,stplhs,stprhs,anorm,sigmax,work,lwork,ifail)
Write (nout,99996) itn
Write (nout,99997) 'Matrix norm =', anorm
Write (nout,99997) 'Final residual norm =', stplhs
Write (nout,*)
! Output x
Write (nout,*) ' X'
Write (nout,99998) x(1:n)
Exit loop
Else
Write (nout,99999) ifail
Exit loop
End If
End Do loop
100 Continue
99999 Format (1X/1X,' ** F11BSF returned with IFAIL = ',I5)
99998 Format (1X,'(',1P,E16.4,',',1P,E16.4,')')
99997 Format (1X,A,1P,E16.3)
99996 Format (1X,'Converged in',I10,' iterations')
End Program f11drfe