Program f04bdfe
! F04BDF Example Program Text
! Mark 29.1 Release. NAG Copyright 2023.
! .. Use Statements ..
Use nag_library, Only: f04bdf, nag_wp, x04caf
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=nag_wp) :: errbnd, rcond
Integer :: i, ierr, ifail, lda, ldb, n, nrhs
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: a(:,:), b(:,:)
! .. Executable Statements ..
Write (nout,*) 'F04BDF Example Program Results'
Write (nout,*)
Flush (nout)
! Skip heading in data file
Read (nin,*)
Read (nin,*) n, nrhs
lda = n
ldb = n
Allocate (a(lda,n),b(ldb,nrhs))
! Read the upper triangular part of A from data file
Read (nin,*)(a(i,i:n),i=1,n)
! Read B from data file
Read (nin,*)(b(i,1:nrhs),i=1,n)
! Solve the equations AX = B for X
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 1
Call f04bdf('Upper',n,nrhs,a,lda,b,ldb,rcond,errbnd,ifail)
If (ifail==0) Then
! Print solution, estimate of condition number and approximate
! error bound
ierr = 0
Call x04caf('General',' ',n,nrhs,b,ldb,'Solution',ierr)
Write (nout,*)
Write (nout,*) 'Estimate of condition number'
Write (nout,99999) 1.0E0_nag_wp/rcond
Write (nout,*)
Write (nout,*) 'Estimate of error bound for computed solutions'
Write (nout,99999) errbnd
Else If (ifail==n+1) Then
! Matrix A is numerically singular. Print estimate of
! reciprocal of condition number and solution
Write (nout,*)
Write (nout,*) 'Estimate of reciprocal of condition number'
Write (nout,99999) rcond
Write (nout,*)
Flush (nout)
ierr = 0
Call x04caf('General',' ',n,nrhs,b,ldb,'Solution',ierr)
Else If (ifail>0 .And. ifail<=n) Then
! The matrix A is not positive definite to working precision
Write (nout,99998) 'The leading minor of order ', ifail, &
' is not positive definite'
Else
Write (nout,99997) ifail
End If
99999 Format (6X,1P,E9.1)
99998 Format (1X,A,I3,A)
99997 Format (1X,' ** F04BDF returned with IFAIL = ',I5)
End Program f04bdfe