Program dporfs_example
! DPORFS Example Program Text
! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com
! .. Use Statements ..
Use lapack_example_aux, Only: nagf_file_print_matrix_real_gen
Use lapack_interfaces, Only: dlacpy, dporfs, dpotrf, dpotrs
Use lapack_precision, Only: dp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, ifail, info, lda, ldaf, ldb, ldx, n, nrhs
Character (1) :: uplo
! .. Local Arrays ..
Real (Kind=dp), Allocatable :: a(:, :), af(:, :), b(:, :), berr(:), &
ferr(:), work(:), x(:, :)
Integer, Allocatable :: iwork(:)
! .. Executable Statements ..
Write (nout, *) 'DPORFS Example Program Results'
! Skip heading in data file
Read (nin, *)
Read (nin, *) n, nrhs
lda = n
ldaf = n
ldb = n
ldx = n
Allocate (a(lda,n), af(ldaf,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 A to AF and B to X
Read (nin, *) uplo
If (uplo=='U') Then
Read (nin, *)(a(i,i:n), i=1, n)
Else If (uplo=='L') Then
Read (nin, *)(a(i,1:i), i=1, n)
End If
Read (nin, *)(b(i,1:nrhs), i=1, n)
Call dlacpy(uplo, n, n, a, lda, af, ldaf)
x(1:n, 1:nrhs) = b(1:n, 1:nrhs)
! Factorize A in the array AF
Call dpotrf(uplo, n, af, ldaf, info)
Write (nout, *)
Flush (nout)
If (info==0) Then
! Compute solution in the array X
Call dpotrs(uplo, n, nrhs, af, ldaf, x, ldx, info)
! Improve solution, and compute backward errors and
! estimated bounds on the forward errors
Call dporfs(uplo, n, nrhs, a, lda, af, ldaf, b, ldb, x, ldx, ferr, &
berr, work, iwork, info)
! Print solution
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call nagf_file_print_matrix_real_gen('General', ' ', n, nrhs, x, ldx, &
'Solution(s)', ifail)
Write (nout, *)
Write (nout, *) 'Backward errors (machine-dependent)'
Write (nout, 100) berr(1:nrhs)
Write (nout, *) 'Estimated forward error bounds (machine-dependent)'
Write (nout, 100) ferr(1:nrhs)
Else
Write (nout, *) 'A is not positive definite'
End If
100 Format ((3X,1P,7E11.1))
End Program