NAG Library Manual, Mark 27.3
Interfaces:  FL   CL   CPP   AD
Program e01eb_t1w_fe

!     E01EB_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: e01ea_t1w_f, e01eb_t1w_f,                       &
x10aa_t1w_f, x10ab_t1w_f, Assignment (=),       &
Operator (*), Operator (+)
Use nag_library, Only: nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Type (c_ptr)                     :: ad_handle
Real (Kind=nag_wp)               :: dx, dy, fr, xr, yr
Integer                          :: ifail, m, n, r
!     .. Local Arrays ..
Type (nagad_t1w_w_rtype), Allocatable :: f(:), pf(:), px(:), py(:),      &
x(:), y(:)
Integer, Allocatable             :: triang(:)
!     .. Executable Statements ..
Write (nout,*) 'E01EB_T1W_F Example Program Results'

!     Skip heading in data file

m = 1
Allocate (f(n),x(n),y(n),px(m),py(m),pf(m),triang(7*n))

!     Initialize x, y and f arrays using data
Do r = 1, n
Read (nin,*) xr, yr, fr
x(r) = xr
y(r) = yr
f(r) = fr
End Do

!     Create AD configuration data object
ifail = 0

!     Call the AD routine
ifail = 0
Call e01ea_t1w_f(n,x,y,triang,ifail)

!     Evaluate interpolant and derivatives at a fixed point
px(1) = 0.5_nag_wp*(x(n/2)+x(n/2+1))
py(1) = 0.5_nag_wp*(y(n/2)+y(n/2+1))

ifail = 0
dx = pf(1)%tangent
px(1)%tangent = 0.0_nag_wp
pf(1) = 0.0_nag_wp

ifail = 0
dy = pf(1)%tangent

Write (nout,*)
Write (nout,99999) 'Interpolation point: x = ', px(1)%value, ' y = ',    &
py(1)%value
Write (nout,99999) 'Interpolated value = ', pf(1)%value
99999 Format (1X,A,F7.4,A,F7.4)

Write (nout,*)
Write (nout,*) ' Derivatives calculated: First order tangents'
Write (nout,*) ' Computational mode    : algorithmic'
Write (nout,*)
Write (nout,*) ' Derivatives of interpolated value w.r.t. fit point'
Write (nout,*)
Write (nout,*) '      d/dx     d/dy'
Write (nout,99998) dx, dy
99998 Format (1X,2(1X,E10.3))

!     Remove computational data object and tape
ifail = 0