```    Program f08jdfe

!     F08JDF Example Program Text

!     Mark 27.1 Release. NAG Copyright 2020.

!     .. Use Statements ..
Use nag_library, Only: dstevr, nag_wp, x04caf
!     .. Implicit None Statement ..
Implicit None
!     .. Parameters ..
Real (Kind=nag_wp), Parameter    :: zero = 0.0_nag_wp
Integer, Parameter               :: nin = 5, nout = 6
!     .. Local Scalars ..
Real (Kind=nag_wp)               :: abstol, vl, vu
Integer                          :: ifail, il, info, iu, ldz, liwork,    &
lwork, m, n
!     .. Local Arrays ..
Real (Kind=nag_wp), Allocatable  :: d(:), e(:), w(:), work(:), z(:,:)
Real (Kind=nag_wp)               :: rdum(1)
Integer                          :: idum(1)
Integer, Allocatable             :: isuppz(:), iwork(:)
!     .. Intrinsic Procedures ..
Intrinsic                        :: max, nint
!     .. Executable Statements ..
Write (nout,*) 'F08JDF Example Program Results'
Write (nout,*)
!     Skip heading in data file and read N and the lower and upper
!     indices of the eigenvalues to be found
Read (nin,*) n, il, iu
ldz = n
m = n
Allocate (d(n),e(n-1),w(n),z(ldz,m),isuppz(2*n))

!     Use routine workspace query to get optimal workspace.
lwork = -1
liwork = -1
!     The NAG name equivalent of dstevr is f08jdf
Call dstevr('Vectors','Indices',n,d,e,vl,vu,il,iu,abstol,m,w,z,ldz,      &
isuppz,rdum,lwork,idum,liwork,info)

!     Make sure that there is enough workspace for block size nb.
lwork = max(20*n,nint(rdum(1)))
liwork = max(10*n,idum(1))
Allocate (work(lwork),iwork(liwork))

!     Read the diagonal and off-diagonal elements of the matrix A
!     from data file

!     Set the absolute error tolerance for eigenvalues.  With ABSTOL
!     set to zero, the default value is used instead

abstol = zero

!     Solve the symmetric tridiagonal eigenvalue problem
!     The NAG name equivalent of dstevr is f08jdf
Call dstevr('Vectors','Indices',n,d,e,vl,vu,il,iu,abstol,m,w,z,ldz,      &
isuppz,work,lwork,iwork,liwork,info)

If (info==0) Then

!       Print solution

Write (nout,*) 'Selected eigenvalues'
Write (nout,99999) w(1:m)
Flush (nout)

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

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

99999 Format (3X,(8F8.4))
99998 Format (1X,A,I5)
End Program f08jdfe
```