NAG Library Manual, Mark 28.5
```    Program f08jhfe

!     F08JHF Example Program Text

!     Mark 28.5 Release. NAG Copyright 2022.

!     .. Use Statements ..
Use nag_library, Only: dsbtrd, dstedc, nag_wp, x04caf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Integer, Parameter               :: nin = 5, nout = 6
Character (1), Parameter         :: uplo = 'U'
!     .. Local Scalars ..
Integer                          :: i, ifail, info, j, kd, ldab, ldz,    &
lgn, liwork, lwork, n
!     .. Local Arrays ..
Real (Kind=nag_wp), Allocatable  :: ab(:,:), d(:), e(:), work(:), z(:,:)
Real (Kind=nag_wp)               :: rdum(1)
Integer                          :: idum(1)
Integer, Allocatable             :: iwork(:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: ceiling, log, max, min, nint, real
!     .. Executable Statements ..
Write (nout,*) 'F08JHF Example Program Results'
Write (nout,*)
!     Skip heading in data file
ldab = kd + 1
ldz = n
lgn = ceiling(log(real(n,kind=nag_wp))/log(2.0E0_nag_wp))
Allocate (ab(ldab,n),d(n),e(n-1),z(ldz,n))

!     Use routine workspace query to get optimal workspace.
lwork = -1
liwork = -1
!     The NAG name equivalent of dstedc is f08jhf
Call dstedc('V',n,d,e,z,ldz,rdum,lwork,idum,liwork,info)

!     Make sure that there is enough workspace.
lwork = max(1+3*n+2*n*lgn+4*n*n,nint(rdum(1)))
liwork = max(6+6*n+5*n*lgn,idum(1))
Allocate (work(lwork),iwork(liwork))

!     Read the upper or lower triangular part of the band matrix 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

!     Reduce A to tridiagonal form T = (Z**T)*A*Z, and form Z
!     The NAG name equivalent of dsbtrd is f08hef
Call dsbtrd('V',uplo,n,kd,ab,ldab,d,e,z,ldz,work,info)

!     Calculate all the eigenvalues and eigenvectors of A,
!     from T and Z
!     The NAG name equivalent of dstedc is f08jhf
Call dstedc('V',n,d,e,z,ldz,work,lwork,iwork,liwork,info)

If (info==0) Then

!       Print eigenvalues and eigenvectors

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

Write (nout,*)
Flush (nout)

!       Standardize the eigenvectors so that first elements are non-negative.
Do i = 1, n
If (z(1,i)<0.0_nag_wp) Then
z(1:n,i) = -z(1:n,i)
End If
End Do

!       ifail: behaviour on error exit
!               =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call x04caf('General',' ',n,n,z,ldz,'Eigenvectors',ifail)

Else
Write (nout,99998) 'Failure in DSTEDC. INFO = ', info
End If

99999 Format ((3X,8F8.4))
99998 Format (1X,A,I10)
End Program f08jhfe
```