NAG Library Manual, Mark 27.2
```    Program f01ec_t1w_fe

!     F01EC_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, x04caf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Integer                          :: i, ifail, j, lda, n
!     .. Local Arrays ..
Type (nagad_t1w_w_rtype), Allocatable :: a(:,:), a_in(:,:)
Real (Kind=nag_wp), Allocatable  :: a_r(:,:)
!     .. Executable Statements ..
Write (nout,*) 'F01EC_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_r(lda,n))
!     Read A from data file
a_in = a_r

!     Create AD configuration data object
ifail = 0

Do i = 1, n
a = a_in
!       ifail: behaviour on error exit
!               =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
!       Find exp( A )
If (i==1) Then
a_r = a
!         Print solution
Call x04caf('General',' ',n,n,a_r,lda,'Exp(A)',ifail)
End If
Do j = 1, n
a_r(i,j) = a(j,j)%tangent
End Do
a_in(i,i)%tangent = 0.0_nag_wp
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,*)
Call x04caf('General',' ',n,n,a_r,n,'       d(expA(i,i))/da(j,j)',ifail)

!     Remove computational data object