!   D02KAF Example Program Text
!   Mark 28.3 Release. NAG Copyright 2022.

    Module d02kafe_mod

!     Data for D02KAF example program

!     .. Use Statements ..
      Use nag_library, Only: nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Accessibility Statements ..
      Private
      Public                           :: coeffn, monit
!     .. Parameters ..
      Real (Kind=nag_wp), Parameter, Public :: one = 1.0_nag_wp
      Real (Kind=nag_wp), Parameter, Public :: zero = 0.0_nag_wp
      Real (Kind=nag_wp), Parameter    :: two = 2.0_nag_wp
      Integer, Parameter, Public       :: nin = 5, nout = 6, qq = 5
    Contains
      Subroutine coeffn(p,q,dqdl,x,elam,jint)

!       .. Scalar Arguments ..
        Real (Kind=nag_wp), Intent (Out) :: dqdl, p, q
        Real (Kind=nag_wp), Intent (In) :: elam, x
        Integer, Intent (In)           :: jint
!       .. Intrinsic Procedures ..
        Intrinsic                      :: cos, real
!       .. Executable Statements ..
        p = one
        dqdl = one
        q = elam - two*real(qq,kind=nag_wp)*cos(two*x)
        Return
      End Subroutine coeffn
      Subroutine monit(nit,iflag,elam,finfo)

!       .. Scalar Arguments ..
        Real (Kind=nag_wp), Intent (In) :: elam
        Integer, Intent (In)           :: iflag, nit
!       .. Array Arguments ..
        Real (Kind=nag_wp), Intent (In) :: finfo(15)
!       .. Executable Statements ..
        If (nit==14) Then
          Write (nout,*)
          Write (nout,*) 'Output from MONIT'
        End If
        Write (nout,99999) nit, iflag, elam, finfo(1:4)
        Return

99999   Format (1X,2I4,F10.3,2E12.2,2F8.1)
      End Subroutine monit
    End Module d02kafe_mod
    Program d02kafe

!     D02KAF Example Main Program

!     .. Use Statements ..
      Use d02kafe_mod, Only: coeffn, monit, nin, nout, one, qq, zero
      Use nag_library, Only: d02kaf, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: delam, delam1, elam, elam1, tol, xl, &
                                          xr
      Integer                          :: i, ifail, k
!     .. Local Arrays ..
      Real (Kind=nag_wp)               :: bcond(3,2)
!     .. Executable Statements ..
      Write (nout,*) 'D02KAF Example Program Results'
!     Skip heading in data file
      Read (nin,*)
!     xl: left-hand end point,  xr: right-hand end point,
!     k: index of the required eigenvalue
!     elam1: initial estimate of the eigenvalue
!     delam1: initial search step
      Read (nin,*) xl, xr
      Read (nin,*) k
      Read (nin,*) elam1, delam1
      bcond(1,1:2) = one
      bcond(2,1:2) = zero
      Do i = 5, 6
        tol = 10.0_nag_wp**(-i)
        elam = elam1
        delam = delam1

!       ifail: behaviour on error exit
!              =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
        ifail = 0
        Call d02kaf(xl,xr,coeffn,bcond,k,tol,elam,delam,monit,ifail)

        Write (nout,*)
        Write (nout,99999) 'Calculation with TOL =', tol
        Write (nout,*)
        Write (nout,*) ' Final results'
        Write (nout,*)
        Write (nout,99998) k, qq, elam, delam
        Write (nout,99997) bcond(3,1), bcond(3,2)
        Write (nout,*)
      End Do

99999 Format (1X,A,E16.4)
99998 Format (1X,' K =',I3,'  QQ =',I3,'  ELAM =',F12.3,'    DELAM =',E12.2)
99997 Format (1X,' BCOND(3,1) =',E12.4,'    BCOND(3,2) =',E12.4)
    End Program d02kafe