NAG Library Manual, Mark 27.2
Program f01fc_t1w_fe

!     F01FC_T1W_F Example Program Text
!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use iso_c_binding, Only: c_ptr
Assignment (=)
Use nag_library, Only: nag_wp, x04daf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Integer                          :: i, ierr, ifail, j, lda, n
!     .. Local Arrays ..
Type (nagad_t1w_w_ctype), Allocatable :: a(:,:), a_in(:,:)
Complex (Kind=nag_wp), Allocatable :: a_c(:,:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: cmplx
!     .. Executable Statements ..
Write (nout,*) 'F01FC_T1W_F Example Program Results'
Write (nout,*)
Flush (nout)
!     Skip heading in data file

lda = n
Allocate (a(lda,n),a_in(lda,n),a_c(lda,n))

!     Read A from data file

a_in = a_c

!     Create AD configuration data object
ifail = 0

Do i = 1, n
a = a_in

!       Find exp( A )
!         ifail: behaviour on error exit
!                =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
a_in(i,i)%vimag%tangent = 0.0_nag_wp

If (i==1) Then
!         Print solution
a_c = a
ierr = 0
Call x04daf('General',' ',n,n,a_c,lda,'Exp(A)',ierr)
End If

Do j = 1, n
a_c(j,i) = cmplx(a(j,j)%vreal%tangent,a(j,j)%vimag%tangent,          &
kind=nag_wp)
End Do
End Do

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

Write (nout,*)
Write (nout,*) ' Derivatives of diagonal of exp(A) w.r.t. diagonal of A'
Write (nout,*)

ierr = 0
Call x04daf('General',' ',n,n,a_c,n,'   d(expA(i,i))/dimag(a(j,j))',     &
ierr)

!     Remove computational data object