Program f08ah_t1w_fe

!     F08AH_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: f08ah_t1w_f, nagad_t1w_get, nagad_t1w_set,      &
                               nagad_t1w_w_rtype, x10aa_t1w_f, x10ab_t1w_f
      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, info, j, lda, lwork, m, n
!     .. Local Arrays ..
      Type (nagad_t1w_w_rtype), Allocatable :: a(:,:), a_in(:,:), tau(:),      &
                                          work(:)
      Real (Kind=nag_wp), Allocatable  :: dlda(:,:), l(:,:)
!     .. Executable Statements ..
      Write (nout,*) 'F08AH_T1W_F Example Program Results'
!     Skip heading in data file
      Read (nin,*)
      Read (nin,*) m, n
      lda = m
      lwork = 64*n
      Allocate (a(lda,n),a_in(lda,n),l(m,m),dlda(m,n),tau(n),work(lwork))

      ifail = 0
      Call x10aa_t1w_f(ad_handle,ifail)

!     Read A from data file

      Read (nin,*)(a_in(i,1:n)%value,i=1,m)
      Do i = 1, m
        Do j = 1, n
          Call nagad_t1w_set(a_in(i,j),0.0_nag_wp,1)
        End Do
      End Do

      a = a_in
      Do i = 1, n
        Call nagad_t1w_set(a(1,i),1.0_nag_wp,1)

!       Compute the LQ factorization of A
!       The NAG name equivalent of dgelqf_t1w is f08ah_t1w_f
        Call f08ah_t1w_f(ad_handle,m,n,a,lda,tau,work,lwork,info)

        Do j = 1, m
          Call nagad_t1w_get(a(j,j),dlda(j,i),1)
        End Do
        If (i==1) Then
          l(1:m,1:m) = a(1:m,1:m)%value
!         Print L

!         ifail: behaviour on error exit
!                =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
          ifail = 0
          Call x04caf('Lower','Non',m,m,l,m,'L from LQ factorization of A',    &
            ifail)
        End If
        a = a_in
      End Do

      Write (nout,*)
      Write (nout,*) 'Derivatives of diagonal of L w.r.t. first row of A'
      ifail = 0
      Call x04caf('General',' ',m,n,dlda,m,'dL_ii/dA_1j',ifail)

!     Remove computational data object
      Call x10ab_t1w_f(ad_handle,ifail)
    End Program f08ah_t1w_fe