Program f07fafe
! F07FAF Example Program Text
! Mark 29.1 Release. NAG Copyright 2023.
! .. Use Statements ..
Use nag_library, Only: dposv, nag_wp, x04caf
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, ifail, info, lda, n
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: a(:,:), b(:)
! .. Executable Statements ..
Write (nout,*) 'F07FAF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
lda = n
Allocate (a(lda,n),b(n))
! 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(1:n)
! Solve the equations Ax = b for x
! The NAG name equivalent of dposv is f07faf
Call dposv('Upper',n,1,a,lda,b,n,info)
If (info==0) Then
! Print solution
Write (nout,*) 'Solution'
Write (nout,99999) b(1:n)
! Print details of factorization
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('Upper','Non-unit diagonal',n,n,a,lda,'Cholesky factor U', &
ifail)
Else
Write (nout,99998) 'The leading minor of order ', info, &
' is not positive definite'
End If
99999 Format ((3X,7F11.4))
99998 Format (1X,A,I3,A)
End Program f07fafe