```!   C06PYF Example Program Text
!   Mark 26.2 Release. NAG Copyright 2017.

Module c06pyfe_mod

!     C06PYF Example Program Module:
!            Parameters and User-defined Routines

!     .. Use Statements ..
Use nag_library, Only: nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Accessibility Statements ..
Private
!     .. Parameters ..
Integer, Parameter, Public       :: nin = 5, nout = 6
Contains

!       .. Scalar Arguments ..
Integer, Intent (In)           :: n1, n2, n3, nin
!       .. Array Arguments ..
Real (Kind=nag_wp), Intent (Out) :: x(n1,n2,n3)
!       .. Local Scalars ..
Integer                        :: i, j, k
!       .. Executable Statements ..
Do i = 1, n1
Do j = 1, n2
End Do
End Do
Return

Subroutine writx(nout,x,n1,n2,n3)
!       Print 3-dimensional real data

!       .. Scalar Arguments ..
Integer, Intent (In)           :: n1, n2, n3, nout
!       .. Array Arguments ..
Real (Kind=nag_wp), Intent (In) :: x(n1,n2,n3)
!       .. Local Scalars ..
Integer                        :: i, j, k
!       .. Executable Statements ..
Do i = 1, n1
Write (nout,*)
Write (nout,99998) 'x(i,j,k) for i =', i
Do j = 1, n2
Write (nout,*)
Write (nout,99999) 'Real ', (x(i,j,k),k=1,n3)
End Do
End Do
Return

99999   Format (1X,A,4F10.3)
99998   Format (1X,A,I6)
End Subroutine writx

Subroutine writy(nout,y,n1,n2,n3)
!       Print 3-dimensional complex data

!       .. Scalar Arguments ..
Integer, Intent (In)           :: n1, n2, n3, nout
!       .. Array Arguments ..
Complex (Kind=nag_wp), Intent (In) :: y(n1,n2,n3)
!       .. Local Scalars ..
Integer                        :: i, j, k
!       .. Intrinsic Procedures ..
Intrinsic                      :: aimag, real
!       .. Executable Statements ..
Do i = 1, n1
Write (nout,*)
Write (nout,99998) 'y(i,j,k) for i =', i
Do j = 1, n2
Write (nout,*)
Write (nout,99999) 'Real ', (real(y(i,j,k)),k=1,n3)
Write (nout,99999) 'Imag ', (aimag(y(i,j,k)),k=1,n3)
End Do
End Do
Return

99999   Format (1X,A,4F10.3)
99998   Format (1X,A,I6)
End Subroutine writy
End Module c06pyfe_mod

Program c06pyfe

!     C06PYF Example Main Program

!     .. Use Statements ..
Use c06pyfe_mod, Only: nin, nout, readx, writx, writy
Use nag_library, Only: c06pyf, c06pzf, nag_wp
!     .. Implicit None Statement ..
Implicit None
!     .. Local Scalars ..
Integer                          :: ieof, ifail, n1, n2, n3
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: y(:)
Real (Kind=nag_wp), Allocatable  :: x(:)
!     .. Executable Statements ..
Write (nout,*) 'C06PYF Example Program Results'
!     Skip heading in data file
loop: Do
If (ieof<0) Then
Exit loop
End If

Allocate (x(n1*n2*n3),y((n1/2+1)*n2*n3))

Write (nout,*)
Write (nout,*) 'Original data values'
Call writx(nout,x,n1,n2,n3)

!       ifail: behaviour on error exit
!              =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
!       -- Compute transform
Call c06pyf(n1,n2,n3,x,y,ifail)

Write (nout,*)
Write (nout,*) 'Components of discrete Fourier transform'
Call writy(nout,y,n1/2+1,n2,n3)

!       -- Compute inverse transform
x = 0._nag_wp
Call c06pzf(n1,n2,n3,y,x,ifail)

Write (nout,*)
Write (nout,*) 'Original sequence as restored by inverse transform'
Call writx(nout,x,n1,n2,n3)
Deallocate (x,y)

End Do loop

End Program c06pyfe
```