NAG Library Manual, Mark 27.2
```    Program f08gnfe

!     F08GNF Example Program Text

!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use nag_library, Only: nag_wp, x02ajf, zhpev
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
Character (1), Parameter         :: uplo = 'U'
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: eerrbd, eps
Integer                          :: i, info, j, n
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: ap(:), work(:)
Complex (Kind=nag_wp)            :: dummy(1,1)
Real (Kind=nag_wp), Allocatable  :: rwork(:), w(:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: abs, max
!     .. Executable Statements ..
Write (nout,*) 'F08GNF Example Program Results'
Write (nout,*)
!     Skip heading in data file

Allocate (ap((n*(n+1))/2),work(2*n-1),rwork(3*n-2),w(n))

!     Read the upper or lower triangular part of the matrix A from
!     data file

If (uplo=='U') Then
Else If (uplo=='L') Then
End If

!     Solve the Hermitian eigenvalue problem

!     The NAG name equivalent of zhpev is f08gnf
Call zhpev('No vectors',uplo,n,ap,w,dummy,1,work,rwork,info)

If (info==0) Then

!       Print solution

Write (nout,*) 'Eigenvalues'
Write (nout,99999) w(1:n)

!       Get the machine precision, EPS and compute the approximate
!       error bound for the computed eigenvalues.  Note that for
!       the 2-norm, max( abs(W(i)) ) = norm(A), and since the
!       eigenvalues are returned in ascending order
!       max( abs(W(i)) ) = max( abs(W(1)), abs(W(n)))

eps = x02ajf()
eerrbd = eps*max(abs(w(1)),abs(w(n)))

!       Print the approximate error bound for the eigenvalues

Write (nout,*)
Write (nout,*) 'Error estimate for the eigenvalues'
Write (nout,99998) eerrbd
Else
Write (nout,99997) 'Failure in ZHPEV. INFO =', info
End If

99999 Format (3X,(8F8.4))
99998 Format (4X,1P,6E11.1)
99997 Format (1X,A,I4)
End Program f08gnfe
```