NAG Library Manual, Mark 29.3
Program f07jufe

!     F07JUF Example Program Text

!     Mark 29.3 Release. NAG Copyright 2023.

!     .. Use Statements ..
Use nag_library, Only: f06upf, nag_wp, x02ajf, zptcon, zpttrf
!     .. 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 ..
Complex (Kind=nag_wp), Allocatable :: e(:)
Real (Kind=nag_wp), Allocatable  :: d(:), rwork(:)
!     .. Executable Statements ..
Write (nout,*) 'F07JUF Example Program Results'
Write (nout,*)
!     Skip heading in data file

Allocate (e(n-1),d(n),rwork(n))

!     Read the lower bidiagonal part of the tridiagonal matrix A from
!     data file

!     Compute the 1-norm of A
anorm = f06upf('1-norm',n,d,e)

!     Factorize the tridiagonal matrix A
!     The NAG name equivalent of zpttrf is f07jrf
Call zpttrf(n,d,e,info)

If (info==0) Then

!       Estimate the condition number of A
!       The NAG name equivalent of zptcon is f07juf
Call zptcon(n,d,e,anorm,rcond,rwork,info)

!       Print the estimated condition number

If (rcond>=x02ajf()) Then
Write (nout,99999) 'Estimate of condition number = ',                &
1.0E0_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 f07jufe