!   E02DE_A1W_F Example Program Text
!   Mark 27.3 Release. NAG Copyright 2021.
    Program e02de_a1w_fe

!     .. Use Statements ..
      Use iso_c_binding, Only: c_ptr
      Use nagad_library, Only: e01da_a1w_f, e02de_a1w_f,                       &
                               nagad_a1w_get_derivative,                       &
                               nagad_a1w_inc_derivative,                       &
                               nagad_a1w_ir_create => x10za_a1w_f,             &
                               nagad_a1w_ir_interpret_adjoint_sparse,          &
                               nagad_a1w_ir_register_variable,                 &
                               nagad_a1w_ir_remove, nagad_a1w_w_rtype,         &
                               x10aa_a1w_f, x10ab_a1w_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                          :: ifail, j, m, mx, my, px, py
!     .. Local Arrays ..
      Type (nagad_a1w_w_rtype), Allocatable :: c(:), f(:,:), lamda(:), mu(:),  &
                                          wrk(:), x(:), y(:)
      Type (nagad_a1w_w_rtype)         :: ff(1), tx(1), ty(1)
      Real (Kind=nag_wp), Allocatable  :: df(:,:), xr(:), yr(:)
      Integer, Allocatable             :: iwrk(:)
!     .. Executable Statements ..
      Write (nout,*) 'E02DE_A1W_F Example Program Results'

!     Skip heading in data file
      Read (nin,*)

!     Read the number of X points, MX, and the values of the
!     X co-ordinates.

      Read (nin,*) mx
      Allocate (x(mx),xr(mx),lamda(mx+4))

      Read (nin,*) xr(1:mx)
      x(1:mx) = xr(1:mx)

!     Read the number of Y points, MY, and the values of the
!     Y co-ordinates.
      Read (nin,*) my

      Allocate (y(my),yr(my),mu(my+4),c(mx*my),f(my,mx),wrk((mx+6)*(my+6)))
      Read (nin,*) yr(1:my)
      y(1:my) = yr(1:my)

!     Read the function values at the grid points.
      Do j = 1, my
        Read (nin,*) xr(1:mx)
        f(j,1:mx) = xr(1:mx)
      End Do

!     Create AD tape
      Call nagad_a1w_ir_create

!     Create AD configuration data object and set computational mode
      ifail = 0
      Call x10aa_a1w_f(ad_handle,ifail)
      ifail = 0

!     Register variables to differentiate w.r.t.
      Call nagad_a1w_ir_register_variable(x)
      Call nagad_a1w_ir_register_variable(y)
      Call nagad_a1w_ir_register_variable(f)

!     Call AD Interpolating Function routine
      ifail = 0
      Call e01da_a1w_f(ad_handle,mx,my,x,y,f,px,py,lamda,mu,c,wrk,ifail)

      Deallocate (wrk)

!     Interpolant to be evaluated at a single point
      m = 1
      tx(1) = 1.4_nag_wp
      ty(1) = 0.5_nag_wp

      Allocate (wrk(py-4),iwrk(py-4))

      ifail = 0
      Call e02de_a1w_f(ad_handle,m,px,py,tx,ty,lamda,mu,c,ff,wrk,iwrk,ifail)

      Write (nout,*)
      Write (nout,99999) tx(1)%value, ty(1)%value
      Write (nout,99998) ff(1)%value
99999 Format (1X,' Spline fitted at point x = ',F6.2,' and y = ',F6.2)
99998 Format (1X,' Value of fitted spline   = ',F7.3)

!     Setup evaluation of derivatives via adjoints
      Call nagad_a1w_inc_derivative(ff(1),1.0_nag_wp)

      ifail = 0
      Call nagad_a1w_ir_interpret_adjoint_sparse(ifail)

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

!     Get derivatives
      xr(1:mx) = nagad_a1w_get_derivative(x)
      yr(1:my) = nagad_a1w_get_derivative(y)
      Allocate (df(my,mx))
      df(1:my,1:mx) = nagad_a1w_get_derivative(f)

      Write (nout,*)
      Write (nout,*) ' Derivatives of fitted value w.r.t. data points:'
      Write (nout,*)
      Call x04caf('General',' ',1,mx,xr,1,' dfit/dx ',ifail)

      Write (nout,*)
      Call x04caf('General',' ',1,my,yr,1,' dfit/dy ',ifail)

      Write (nout,*)
      Write (nout,*) ' Derivatives of fitted value w.r.t. f-values:'
      Write (nout,*)
      Call x04caf('General',' ',my,mx,df,my,' dfit/df ',ifail)

!     Remove computational data object and tape
      Call x10ab_a1w_f(ad_handle,ifail)
      Call nagad_a1w_ir_remove

    End Program e02de_a1w_fe