NAG Library Manual, Mark 30.1
Interfaces:  FL   CL   CPP   AD
```    Program f08hqfe

!     F08HQF Example Program Text

!     Mark 30.1 Release. NAG Copyright 2024.

!     .. Use Statements ..
Use nag_library, Only: dznrm2, nag_wp, x04daf, zhbevd
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Complex (Kind=nag_wp)            :: scal
Integer                          :: i, ifail, info, j, k, kd, ldab, ldz, &
liwork, lrwork, lwork, n
Character (1)                    :: job, uplo
!     .. Local Arrays ..
Complex (Kind=nag_wp), Allocatable :: ab(:,:), work(:), z(:,:)
Real (Kind=nag_wp), Allocatable  :: rwork(:), w(:)
Integer, Allocatable             :: iwork(:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: abs, conjg, max, maxloc, min
!     .. Executable Statements ..
Write (nout,*) 'F08HQF Example Program Results'
!     Skip heading in data file
Read (nin,*) n, kd
ldab = n
ldz = n
liwork = 5*n + 3
lrwork = 2*n*n + 5*n + 1
lwork = 2*n*n
Allocate (ab(ldab,n),work(lwork),z(ldz,n),rwork(lrwork),w(n),            &
iwork(liwork))

!     Read A from data file

If (uplo=='U') Then
Do i = 1, n
End Do
Else If (uplo=='L') Then
Do i = 1, n
End Do
End If

!     Calculate all the eigenvalues and eigenvectors of A
!     The NAG name equivalent of zhbevd is f08hqf
Call zhbevd(job,uplo,n,kd,ab,ldab,w,z,ldz,work,lwork,rwork,lrwork,iwork, &
liwork,info)

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

!       Print eigenvalues and eigenvectors

Write (nout,*) 'Eigenvalues'
Do i = 1, n
Write (nout,99999) i, w(i)
End Do
Write (nout,*)
Flush (nout)

!       Normalize the eigenvectors, largest element real
Do i = 1, n
rwork(1:n) = abs(z(1:n,i))
k = maxloc(rwork(1:n),1)
scal = conjg(z(k,i))/abs(z(k,i))/dznrm2(n,z(1,i),1)
z(1:n,i) = z(1:n,i)*scal
End Do

!       ifail: behaviour on error exit
!              =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04daf('General',' ',n,n,z,ldz,'Eigenvectors',ifail)

End If

99999 Format (3X,I5,5X,2F8.4)
End Program f08hqfe
```