Program f07fhfe
! F07FHF Example Program Text
! Mark 30.2 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: dporfs, dpotrf, dpotrs, f06qff, nag_wp, x04caf
! .. 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=nag_wp), Allocatable :: a(:,:), af(:,:), b(:,:), berr(:), &
ferr(:), work(:), x(:,:)
Integer, Allocatable :: iwork(:)
! .. Executable Statements ..
Write (nout,*) 'F07FHF 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 f06qff(uplo,n,n,a,lda,af,ldaf)
x(1:n,1:nrhs) = b(1:n,1:nrhs)
! Factorize A in the array AF
! The NAG name equivalent of dpotrf is f07fdf
Call dpotrf(uplo,n,af,ldaf,info)
Write (nout,*)
Flush (nout)
If (info==0) Then
! Compute solution in the array X
! The NAG name equivalent of dpotrs is f07fef
Call dpotrs(uplo,n,nrhs,af,ldaf,x,ldx,info)
! Improve solution, and compute backward errors and
! estimated bounds on the forward errors
! The NAG name equivalent of dporfs is f07fhf
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 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)
Else
Write (nout,*) 'A is not positive definite'
End If
99999 Format ((3X,1P,7E11.1))
End Program f07fhfe