Program f07fd_t1w_fe

!     F07FD_T1W_F Example Program Text
!     Mark 27.3 Release. NAG Copyright 2021.

!     .. Use Statements ..
      Use iso_c_binding, Only: c_ptr
      Use nagad_library, Only: f07fd_t1w_f, nagad_t1w_w_rtype, x10aa_t1w_f,    &
                               x10ab_t1w_f, Assignment (=)
      Use nag_library, Only: nag_wp, x04caf
!     .. Implicit None Statement ..
      Implicit None
!     .. Parameters ..
      Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
      Type (c_ptr)                     :: ad_handle
      Integer                          :: i, ifail, j, lda, n
      Character (1)                    :: uplo
!     .. Local Arrays ..
      Type (nagad_t1w_w_rtype), Allocatable :: a(:,:), ax(:,:)
      Real (Kind=nag_wp), Allocatable  :: ar(:,:), ddda(:,:)
!     .. Executable Statements ..
      Write (nout,*) 'F07FD_T1W_F Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) n
      lda = n
      Allocate (a(lda,n),ax(lda,n))
      Allocate (ar(lda,n),ddda(n,n))

!     Read A from data file

      ar = 0.0_nag_wp
      Read (nin,*) uplo
      If (uplo=='U') Then
        Read (nin,*)(ar(i,i:n),i=1,n)
      Else If (uplo=='L') Then
        Read (nin,*)(ar(i,1:i),i=1,n)
      End If
      a = ar

!     Create AD configuration data object
      ifail = 0
      Call x10aa_t1w_f(ad_handle,ifail)

      Do i = 1, n
        a(i,1)%tangent = 1.0_nag_wp

        ax = a
!       Factorize A
!       The NAG name equivalent of dpotrf_t1w is f07fd_t1w_f
        ifail = 0
        Call f07fd_t1w_f(ad_handle,uplo,n,ax,lda,ifail)

        a(i,1)%tangent = 0.0_nag_wp

        Do j = 1, n
          ddda(j,i) = ax(j,j)%tangent
        End Do
      End Do

!     Print L or U from factorization
      Write (nout,*)
      Flush (nout)

      ar(1:n,1:n) = ax(1:n,1:n)%value
      ifail = 0
      Call x04caf(uplo,'Nonunit',n,n,ar,lda,'Factor',ifail)

      Write (nout,*)
      Write (nout,*) ' Derivatives calculated: First order tangents'
      Write (nout,*) ' Computational mode    : algorithmic'

      Write (nout,*)
      Write (nout,*) ' Derivatives of diagonal of L w.r.t. first column of A:'
      Call x04caf('General',' ',n,n,ddda,n,'',ifail)

!     Remove computational data object
      Call x10ab_t1w_f(ad_handle,ifail)

    End Program f07fd_t1w_fe