Program f07fgfe
! F07FGF Example Program Text
! Mark 30.1 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: dlansy => f06rcf, dpocon, dpotrf, nag_wp, x02ajf
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=nag_wp) :: anorm, rcond
Integer :: i, info, lda, n
Character (1) :: uplo
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: a(:,:), work(:)
Integer, Allocatable :: iwork(:)
! .. Executable Statements ..
Write (nout,*) 'F07FGF Example Program Results'
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
lda = n
Allocate (a(lda,n),work(3*n),iwork(n))
! Read A from data file
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
! Compute norm of A
! f06rcf is the NAG name equivalent of the LAPACK auxiliary dlansy
anorm = dlansy('1-norm',uplo,n,a,lda,work)
! Factorize A
! The NAG name equivalent of dpotrf is f06fdf
Call dpotrf(uplo,n,a,lda,info)
Write (nout,*)
If (info==0) Then
! Estimate condition number
! The NAG name equivalent of dpocon is f07fgf
Call dpocon(uplo,n,a,lda,anorm,rcond,work,iwork,info)
If (rcond>=x02ajf()) Then
Write (nout,99999) 'Estimate of condition number =', &
1.0_nag_wp/rcond
Else
Write (nout,*) 'A is singular to working precision'
End If
Else
Write (nout,*) 'A is not positive definite'
End If
99999 Format (1X,A,1P,E10.2)
End Program f07fgfe