Program f07wdfe

!     F07WDF Example Program Text

!     Mark 30.2 Release. NAG Copyright 2024.

!     .. Use Statements ..
      Use nag_library, Only: dpftrf, dtfttr, nag_wp, x04caf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Integer                          :: i, ifail, info, k, lar1, lda, lenar, &
                                          n, q
      Character (1)                    :: transr, uplo
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: a(:,:), ar(:)
!     .. Executable Statements ..
      Write (nout,*) 'F07WDF Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n, uplo, transr

      lenar = n*(n+1)/2
      lda = n
      Allocate (ar(lenar),a(lda,n))

!     Setup notional dimensions of RFP matrix AR
      k = n/2
      q = n - k
      If (transr=='N' .Or. transr=='n') Then
        lar1 = 2*k + 1
      Else
        lar1 = q
      End If

!     Read an RFP matrix into array AR
      Do i = 1, lar1
        Read (nin,*) ar(i:lenar:lar1)
      End Do

!     Factorize A
!     The NAG name equivalent of dpftrf is f07wdf
      Call dpftrf(transr,uplo,n,ar,info)

      Write (nout,*)
      Flush (nout)
      If (info==0) Then

!       Convert factor to full array form, and print it
!       The NAG name equivalent of dtfttr is f01vgf
        Call dtfttr(transr,uplo,n,ar,a,lda,info)
        ifail = 0
        Call x04caf(uplo,'Nonunit',n,n,a,lda,'Factor',ifail)

      Else
        Write (nout,*) 'A is not positive definite'
      End If

    End Program f07wdfe