```    Program f08ntfe

!     F08NTF Example Program Text

!     Mark 26.2 Release. NAG Copyright 2017.

!     .. Use Statements ..
Use nag_library, Only: nag_wp, x02ajf, x04dbf, zgehrd, zgemm, zhseqr,    &
zlange => f06uaf, zunghr
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Complex (Kind=nag_wp)            :: alpha, beta
Real (Kind=nag_wp)               :: norm
Integer                          :: i, ifail, info, lda, ldc, ldd, ldz,  &
lwork, n
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: a(:,:), c(:,:), d(:,:), tau(:),    &
w(:), work(:), z(:,:)
Real (Kind=nag_wp), Allocatable  :: rwork(:)
Character (1)                    :: clabs(1), rlabs(1)
!     .. Intrinsic Procedures ..
Intrinsic                        :: cmplx
!     .. Executable Statements ..
Write (nout,*) 'F08NTF Example Program Results'
Write (nout,*)
Flush (nout)
!     Skip heading in data file
lda = n
ldc = n
ldd = n
ldz = n
lwork = 64*(n-1)
Allocate (a(lda,n),c(ldc,n),d(ldd,n),rwork(lda),tau(n),w(n),work(lwork), &
z(ldz,n))

!     Read A from data file

!     Store A in D
d(1:ldd,1:n) = a(1:lda,1:n)

!     Print matrix A
!     ifail: behaviour on error exit
!            =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04dbf('General',' ',n,n,a,lda,'Bracketed','F7.4','Matrix A',       &
'Integer',rlabs,'Integer',clabs,80,0,ifail)
Write (nout,*)
Flush (nout)

!     Reduce A to upper Hessenberg form H = (Q**H)*A*Q

!     The NAG name equivalent of zgehrd is f08nsf
Call zgehrd(n,1,n,a,lda,tau,work,lwork,info)

!     Copy A into Z
z(1:n,1:n) = a(1:n,1:n)

!     Form Q explicitly, storing the result in Z
!     The NAG name equivalent of zunghr is f08ntf
Call zunghr(n,1,n,z,ldz,tau,work,lwork,info)

!     Calculate the Schur factorization of H = Y*T*(Y**H) and form
!     Q*Y explicitly, storing the result in Z

!     Note that A = Z*T*(Z**H), where Z = Q*Y

!     The NAG name equivalent of zhseqr is f08psf
Call zhseqr('Schur form','Vectors',n,1,n,a,lda,w,z,ldz,work,lwork,info)

!     Compute A - Z*T*Z^H from Schur factorization of A, and store in matrix D
!     The NAG name equivalent of zgemm is f06zaf
alpha = cmplx(1,kind=nag_wp)
beta = cmplx(0,kind=nag_wp)
Call zgemm('N','N',n,n,n,alpha,z,ldz,a,lda,beta,c,ldc)
alpha = cmplx(-1,kind=nag_wp)
beta = cmplx(1,kind=nag_wp)
Call zgemm('N','C',n,n,n,alpha,c,ldc,z,ldz,beta,d,ldd)

!     Find norm of matrix D and print warning if it is too large
!     f06uaf is the NAG name equivalent of the LAPACK auxiliary zlange
norm = zlange('O',ldd,n,d,ldd,rwork)
If (norm>x02ajf()**0.5_nag_wp) Then
Write (nout,*) 'Norm of A-(Z*T*Z^H) is much greater than 0.'
Write (nout,*) 'Schur factorization has failed.'
Else
!       Print eigenvalues.
Write (nout,*) 'Eigenvalues'
Write (nout,99999)(w(i),i=1,n)
End If

99999 Format ((3X,4(' (',F7.4,',',F7.4,')',:)))

End Program f08ntfe
```