Program f07nnfe
! F07NNF Example Program Text
! Mark 30.2 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: nag_wp, x04dbf, zsysv
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nb = 64, nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, ifail, info, lda, lwork, n
! .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: a(:,:), b(:), work(:)
Integer, Allocatable :: ipiv(:)
Character (1) :: clabs(1), rlabs(1)
! .. Executable Statements ..
Write (nout,*) 'F07NNF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
lda = n
lwork = nb*n
Allocate (a(lda,n),b(n),work(lwork),ipiv(n))
! Read the upper triangular part of the matrix 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 zsysv is f07nnf
Call zsysv('Upper',n,1,a,lda,ipiv,b,n,work,lwork,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 x04dbf('Upper','Non-unit diagonal',n,n,a,lda,'Bracketed','F7.4', &
'Details of the factorization','Integer',rlabs,'Integer',clabs,80,0, &
ifail)
! Print pivot indices
Write (nout,*)
Write (nout,*) 'Pivot indices'
Write (nout,99998) ipiv(1:n)
Else
Write (nout,99997) 'The diagonal block ', info, ' of D is zero'
End If
99999 Format ((4X,4('(',F7.4,',',F7.4,') ')))
99998 Format (1X,7I11)
99997 Format (1X,A,I3,A)
End Program f07nnfe