!   D01GBF Example Program Text
!   Mark 28.7 Release. NAG Copyright 2022.

    Module d01gbfe_mod

!     D01GBF Example Program Module:
!            Parameters and User-defined Routines

!     .. Use Statements ..
      Use nag_library, Only: nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Accessibility Statements ..
      Private
      Public                           :: f
!     .. Parameters ..
      Integer, Parameter, Public       :: lenwrk = 500, maxcls = 20000,        &
                                          ndim = 4, nout = 6
    Contains
      Function f(ndim,x)

!       .. Function Return Value ..
        Real (Kind=nag_wp)             :: f
!       .. Scalar Arguments ..
        Integer, Intent (In)           :: ndim
!       .. Array Arguments ..
        Real (Kind=nag_wp), Intent (In) :: x(ndim)
!       .. Intrinsic Procedures ..
        Intrinsic                      :: exp
!       .. Executable Statements ..
        f = 4.0E0_nag_wp*x(1)*x(3)**2*exp(2.0E0_nag_wp*x(1)*x(3))/             &
          (1.0E0_nag_wp+x(2)+x(4))**2

        Return

      End Function f
    End Module d01gbfe_mod
    Program d01gbfe

!     D01GBF Example Main Program

!     .. Use Statements ..
      Use d01gbfe_mod, Only: f, lenwrk, maxcls, ndim, nout
      Use nag_library, Only: d01gbf, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: acc, eps, finest
      Integer                          :: ifail, mincls
!     .. Local Arrays ..
      Real (Kind=nag_wp), Allocatable  :: a(:), b(:), wrkstr(:)
!     .. Executable Statements ..
      Write (nout,*) 'D01GBF Example Program Results'

      Allocate (a(ndim),b(ndim),wrkstr(lenwrk))

      a(1:ndim) = 0.0E0_nag_wp
      b(1:ndim) = 1.0E0_nag_wp
      eps = 0.01E0_nag_wp
      mincls = 1000

      ifail = -1
      Call d01gbf(ndim,a,b,mincls,maxcls,f,eps,acc,lenwrk,wrkstr,finest,ifail)

      Select Case (ifail)
      Case (0,2)
        Write (nout,*)
        Write (nout,99998) 'Requested accuracy    = ', eps
        Write (nout,99997) 'Estimated value       = ', finest
        Write (nout,99998) 'Estimated accuracy    = ', acc
        Write (nout,99999) 'Number of evaluations = ', mincls
      End Select

99999 Format (1X,A,I5)
99998 Format (1X,A,E13.2)
99997 Format (1X,A,F13.5)
    End Program d01gbfe