Program dppsv_example

!     DPPSV 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_packed
      Use lapack_interfaces, Only: dppsv
      Use lapack_precision, Only: dp
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter :: nin = 5, nout = 6
      Character (1), Parameter :: uplo = 'U'
!     .. Local Scalars ..
      Integer :: i, ifail, info, j, n
!     .. Local Arrays ..
      Real (Kind=dp), Allocatable :: ap(:), b(:)
!     .. Executable Statements ..
      Write (nout, *) 'DPPSV Example Program Results'
      Write (nout, *)
!     Skip heading in data file
      Read (nin, *)
      Read (nin, *) n

      Allocate (ap((n*(n+1))/2), b(n))

!     Read the upper or lower triangular part of the matrix A from
!     data file

      If (uplo=='U') Then
        Read (nin, *)((ap(i+(j*(j-1))/2),j=i,n), i=1, n)
      Else If (uplo=='L') Then
        Read (nin, *)((ap(i+((2*n-j)*(j-1))/2),j=1,i), i=1, n)
      End If

!     Read b from data file

      Read (nin, *) b(1:n)

!     Solve the equations Ax = b for x
      Call dppsv(uplo, n, 1, ap, b, n, info)

      If (info==0) Then

!       Print solution

        Write (nout, *) 'Solution'
        Write (nout, 100) 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 nagf_file_print_matrix_real_packed(uplo, 'Non-unit diagonal', n, &
          ap, 'Cholesky factor', ifail)

      Else
        Write (nout, 110) 'The leading minor of order ', info, &
          ' is not positive definite'
      End If

100   Format ((3X,7F11.4))
110   Format (1X, A, I3, A)
    End Program