!   D01JAF Example Program Text
!   Mark 27.2 Release. NAG Copyright 2021.

    Module d01jafe_mod

!     D01JAF Example Program Module:
!            Parameters and User-defined Routines

!     .. Use Statements ..
      Use nag_library, Only: nag_wp, x02amf
!     .. Implicit None Statement ..
      Implicit None
!     .. Accessibility Statements ..
      Private
      Public                           :: f
!     .. Parameters ..
      Integer, Parameter, Public       :: 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)
!       .. Local Scalars ..
        Real (Kind=nag_wp)             :: a, rho
!       .. Intrinsic Procedures ..
        Intrinsic                      :: abs, sqrt
!       .. Executable Statements ..
        rho = x(1)
        a = (1.0E0_nag_wp-rho)*(1.0E0_nag_wp+rho)

        If (abs(a)>=x02amf()) Then
          f = 1.0E0_nag_wp/sqrt(a)
        Else
          f = 0.0E0_nag_wp
        End If

        Return

      End Function f
    End Module d01jafe_mod
    Program d01jafe

!     D01JAF Example Main Program

!     .. Use Statements ..
      Use d01jafe_mod, Only: f, nout
      Use nag_library, Only: d01jaf, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: epsa, epsr, esterr, radius, relest,  &
                                          result
      Integer                          :: icoord, ifail, method, ndim, nevals
!     .. Executable Statements ..
      Write (nout,*) 'D01JAF Example Program Results'

      radius = 1.0E0_nag_wp
      method = 0
      icoord = 1
      epsa = 0.0E0_nag_wp
      epsr = 0.5E-4_nag_wp

test: Do ndim = 2, 4, 2

        ifail = -1
        Call d01jaf(f,ndim,radius,epsa,epsr,method,icoord,result,esterr,       &
          nevals,ifail)

        Select Case (ifail)
        Case (:-1)
          Exit test
        Case (0:3)
          relest = esterr/result
          Write (nout,*)
          Write (nout,99999) 'Dimension of the sphere       =', ndim
          Write (nout,99998) 'Requested relative tolerance  =', epsr
          Write (nout,99997) 'Approximation to the integral =', result
          Write (nout,99999) 'No. of function evaluations   =', nevals
          Write (nout,99998) 'Estimated relative error      =', relest
        End Select

      End Do test

99999 Format (1X,A,I5)
99998 Format (1X,A,E9.2)
99997 Format (1X,A,F9.5)
    End Program d01jafe