Program f11dkfe

!     F11DKF Example Program Text

!     Mark 30.3 Release. nAG Copyright 2024.

!     .. Use Statements ..
      Use nag_library, Only: f11bdf, f11bef, f11bff, f11dkf, f11xaf, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: anorm, sigmax, stplhs, stprhs, tol
      Integer                          :: i, ifail, ifail1, irevcm, iterm,     &
                                          itn, lwork, lwreq, m, maxitn, monit, &
                                          n, niter, nnz
      Character (1)                    :: init, norm, precon, weight
      Character (8)                    :: method
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: a(:), b(:), diag(:), wgt(:),         &
                                          work(:), x(:)
      Integer, Allocatable             :: icol(:), irow(:)
!     .. Executable Statements ..
      Write (nout,*) 'F11DKF Example Program Results'

!     Skip heading in data file

      Read (nin,*)
      Read (nin,*) n
      Read (nin,*) nnz
      lwork = 200
      Allocate (a(nnz),b(n),diag(n),wgt(n),work(lwork),x(n),icol(nnz),         &
        irow(nnz))

!     Read or initialize the parameters for the iterative solver

      Read (nin,*) method
      Read (nin,*) precon, norm, weight, iterm
      Read (nin,*) m, tol, maxitn
      Read (nin,*) monit
      anorm = 0.0E0_nag_wp
      sigmax = 0.0E0_nag_wp

!     Read the parameters for the preconditioner

      Read (nin,*) niter

!     Read the nonzero elements of the matrix A

      Do i = 1, nnz
        Read (nin,*) a(i), irow(i), icol(i)
      End Do

!     Read right-hand side vector b and initial approximate solution

      Read (nin,*) b(1:n)
      Read (nin,*) x(1:n)

!     Call F11BDF to initialize the solver

!       ifail: behaviour on error exit
!                =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
      ifail = 0
      Call f11bdf(method,precon,norm,weight,iterm,n,m,tol,maxitn,anorm,sigmax, &
        monit,lwreq,work,lwork,ifail)

!     Call repeatedly F11BEF to solve the equations
!     Note that the arrays B and X are overwritten

!     On final exit, X will contain the solution and B the residual
!     vector

      irevcm = 0
      init = 'I'

      ifail = 1
loop: Do
        Call f11bef(irevcm,x,b,wgt,work,lwreq,ifail)

        If (irevcm/=4) Then
          ifail1 = -1
          Select Case (irevcm)
          Case (-1)

            Call f11xaf('Transpose',n,nnz,a,irow,icol,'No checking',x,b,       &
              ifail1)

          Case (1)

            Call f11xaf('No transpose',n,nnz,a,irow,icol,'No checking',x,b,    &
              ifail1)

          Case (2)

            Call f11dkf('Non symmetric','N',init,niter,n,nnz,a,irow,icol,      &
              'Check',x,b,diag,work(lwreq+1),ifail1)

            init = 'N'
          Case (3)

            ifail1 = 0
            Call f11bff(itn,stplhs,stprhs,anorm,sigmax,work,lwreq,ifail1)

            Write (nout,99999) itn, stplhs
          End Select
          If (ifail1/=0) Then
            irevcm = 6
          End If
        Else If (ifail/=0) Then
          Write (nout,99993) ifail
          Go To 100
        Else
          Exit loop
        End If
      End Do loop

!     Obtain information about the computation

      ifail1 = 0
      Call f11bff(itn,stplhs,stprhs,anorm,sigmax,work,lwreq,ifail1)

!     Print the output data
      Write (nout,99996)
      Write (nout,99995) 'Number of iterations for convergence:    ', itn
      Write (nout,99994) 'Residual norm:                           ', stplhs
      Write (nout,99994) 'Right-hand side of termination criterion:', stprhs
      Write (nout,99994) '1-norm of matrix A:                      ', anorm

!     Output x

      Write (nout,99998)
      Write (nout,99997)(x(i),b(i),i=1,n)
100   Continue

99999 Format (/,1X,'Monitoring at iteration no.',I4,/,1X,1P,'residual no',     &
        'rm: ',E14.4)
99998 Format (/,2X,'  Solution vector',2X,' Residual vector')
99997 Format (1X,1P,E16.4,1X,E16.4)
99996 Format (/,1X,'Final Results')
99995 Format (1X,A,I4)
99994 Format (1X,A,1P,E14.4)
99993 Format (1X,/,1X,' ** F11BEF returned with IFAIL = ',I5)
    End Program f11dkfe