NAG Library Manual, Mark 27.2
```    Program f08ssfe

!     F08SSF Example Program Text

!     Mark 27.2 Release. NAG Copyright 2021.

!     .. Use Statements ..
Use nag_library, Only: dsterf, nag_wp, zhegst, zhetrd, zpotrf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Integer                          :: i, info, lda, ldb, lwork, n
Character (1)                    :: uplo
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: a(:,:), b(:,:), tau(:), work(:)
Real (Kind=nag_wp), Allocatable  :: d(:), e(:)
!     .. Executable Statements ..
Write (nout,*) 'F08SSF Example Program Results'
!     Skip heading in data file
lda = n
ldb = n
lwork = 64*n
Allocate (a(lda,n),b(ldb,n),tau(n),work(lwork),d(n),e(n-1))

!     Read A and B from data file

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

!     Compute the Cholesky factorization of B
!     The NAG name equivalent of zpotrf is f07frf
Call zpotrf(uplo,n,b,ldb,info)

Write (nout,*)
If (info>0) Then
Write (nout,*) 'B is not positive definite.'
Else

!       Reduce the problem to standard form C*y = lambda*y, storing
!       the result in A
!       The NAG name equivalent of zhegst is f08ssf
Call zhegst(1,uplo,n,a,lda,b,ldb,info)

!       Reduce C to tridiagonal form T = (Q**H)*C*Q
!       The NAG name equivalent of zhetrd is f08fsf
Call zhetrd(uplo,n,a,lda,d,e,tau,work,lwork,info)

!       Calculate the eigenvalues of T (same as C)
!       The NAG name equivalent of dsterf is f08jff
Call dsterf(n,d,e,info)

If (info>0) Then
Write (nout,*) 'Failure to converge.'
Else

!         Print eigenvalues

Write (nout,*) 'Eigenvalues'
Write (nout,99999) d(1:n)
End If
End If

99999 Format (3X,(9F8.4))
End Program f08ssfe
```