Program f07vhfe

!     F07VHF Example Program Text

!     Mark 28.6 Release. NAG Copyright 2022.

!     .. Use Statements ..
      Use nag_library, Only: dtbrfs, dtbtrs, nag_wp, x04caf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
      Character (1), Parameter         :: diag = 'N', trans = 'N'
!     .. Local Scalars ..
      Integer                          :: i, ifail, info, j, kd, ldab, ldb,    &
                                          ldx, n, nrhs
      Character (1)                    :: uplo
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: ab(:,:), b(:,:), berr(:), ferr(:),   &
                                          work(:), x(:,:)
      Integer, Allocatable             :: iwork(:)
!     .. Intrinsic Procedures ..
      Intrinsic                        :: max, min
!     .. Executable Statements ..
      Write (nout,*) 'F07VHF Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n, kd, nrhs
      ldab = kd + 1
      ldb = n
      ldx = n
      Allocate (ab(ldab,n),b(ldb,nrhs),berr(nrhs),ferr(nrhs),work(3*n),        &
        x(ldx,n),iwork(n))

!     Read A and B from data file, and copy B to X

      Read (nin,*) uplo
      If (uplo=='U') Then
        Do i = 1, n
          Read (nin,*)(ab(kd+1+i-j,j),j=i,min(n,i+kd))
        End Do
      Else If (uplo=='L') Then
        Do i = 1, n
          Read (nin,*)(ab(1+i-j,j),j=max(1,i-kd),i)
        End Do
      End If
      Read (nin,*)(b(i,1:nrhs),i=1,n)

      x(1:n,1:nrhs) = b(1:n,1:nrhs)

!     Compute solution in the array X
!     The NAG name equivalent of dtbtrs is f07vef
      Call dtbtrs(uplo,trans,diag,n,kd,nrhs,ab,ldab,x,ldx,info)

!     Compute backward errors and estimated bounds on the
!     forward errors

!     The NAG name equivalent of dtbrfs is f07vhf
      Call dtbrfs(uplo,trans,diag,n,kd,nrhs,ab,ldab,b,ldb,x,ldx,ferr,berr,     &
        work,iwork,info)

!     Print solution

      Write (nout,*)
      Flush (nout)

!     ifail: behaviour on error exit
!             =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
      ifail = 0
      Call x04caf('General',' ',n,nrhs,x,ldx,'Solution(s)',ifail)

      Write (nout,*)
      Write (nout,*) 'Backward errors (machine-dependent)'
      Write (nout,99999) berr(1:nrhs)
      Write (nout,*) 'Estimated forward error bounds (machine-dependent)'
      Write (nout,99999) ferr(1:nrhs)

99999 Format ((3X,1P,7E11.1))
    End Program f07vhfe