Program f07jgfe
! F07JGF Example Program Text
! Mark 30.0 Release. NAG Copyright 2024.
! .. Use Statements ..
Use nag_library, Only: dptcon, dpttrf, f06rpf, nag_wp, x02ajf
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=nag_wp) :: anorm, rcond
Integer :: info, n
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: d(:), e(:), work(:)
! .. Executable Statements ..
Write (nout,*) 'F07JGF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
Read (nin,*) n
Allocate (d(n),e(n-1),work(n))
! Read the lower bidiagonal part of the tridiagonal matrix A from
! data file
Read (nin,*) d(1:n)
Read (nin,*) e(1:n-1)
! Compute the 1-norm of A
anorm = f06rpf('1-norm',n,d,e)
! Factorize the tridiagonal matrix A
! The NAG name equivalent of dpttrf is f07jdf
Call dpttrf(n,d,e,info)
If (info==0) Then
! Estimate the condition number of A
! The NAG name equivalent of dptcon is f07jgf
Call dptcon(n,d,e,anorm,rcond,work,info)
! Print the estimated condition number
If (rcond>=x02ajf()) Then
Write (nout,99999) 'Estimate of condition number = ', &
1.0_nag_wp/rcond
Else
Write (nout,99999) 'A is singular to working precision. RCOND = ', &
rcond
End If
Else
Write (nout,99998) 'The leading minor of order ', info, &
' is not positive definite'
End If
99999 Format (1X,A,1P,E10.2)
99998 Format (1X,A,I3,A)
End Program f07jgfe