Program dpttrs_example
! DPTTRS Example Program Text
! Copyright 2017, Numerical Algorithms Group Ltd. http://www.nag.com
! .. Use Statements ..
Use lapack_example_aux, Only: nagf_file_print_matrix_real_gen
Use lapack_interfaces, Only: dpttrf, dpttrs
Use lapack_precision, Only: dp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Integer :: i, ifail, info, ldb, n, nrhs
! .. Local Arrays ..
Real (Kind=dp), Allocatable :: b(:, :), d(:), e(:)
! .. Executable Statements ..
Write (nout, *) 'DPTTRS Example Program Results'
Write (nout, *)
Flush (nout)
! Skip heading in data file
Read (nin, *)
Read (nin, *) n, nrhs
ldb = n
Allocate (b(ldb,nrhs), d(n), e(n-1))
! Read the upper bidiagonal part of the tridiagonal matrix A from
! data file
Read (nin, *) e(1:n-1)
Read (nin, *) d(1:n)
! Read the right hand matrix B
Read (nin, *)(b(i,1:nrhs), i=1, n)
! Factorize the tridiagonal matrix A
Call dpttrf(n, d, e, info)
If (info==0) Then
! Solve the equations AX = B
Call dpttrs(n, nrhs, d, e, b, ldb, info)
! Print the solution
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call nagf_file_print_matrix_real_gen('General', ' ', n, nrhs, b, ldb, &
'Solution(s)', ifail)
Else
Write (nout, 100) 'The leading minor of order ', info, &
' is not positive definite'
End If
100 Format (1X, A, I3, A)
End Program