!   C05AZF Example Program Text
!   Mark 27.3 Release. NAG Copyright 2021.

    Module c05azfe_mod

!     C05AZF 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 ..
      Real (Kind=nag_wp), Parameter, Public :: tolx = 1.0E-5_nag_wp
      Integer, Parameter, Public       :: ir = 0, nout = 6
    Contains
      Function f(x)

!       .. Function Return Value ..
        Real (Kind=nag_wp)             :: f
!       .. Scalar Arguments ..
        Real (Kind=nag_wp), Intent (In) :: x
!       .. Intrinsic Procedures ..
        Intrinsic                      :: exp
!       .. Executable Statements ..
        f = exp(-x) - x

        Return

      End Function f
    End Module c05azfe_mod
    Program c05azfe

!     C05AZF Example Main Program

!     .. Use Statements ..
      Use c05azfe_mod, Only: f, ir, nout, tolx
      Use nag_library, Only: c05azf, nag_wp
!     .. Implicit None Statement ..
      Implicit None
!     .. Local Scalars ..
      Real (Kind=nag_wp)               :: fx, x, y
      Integer                          :: ifail, ind
!     .. Local Arrays ..
      Real (Kind=nag_wp)               :: c(17)
!     .. Executable Statements ..
      Write (nout,*) 'C05AZF Example Program Results'

      Write (nout,*)
      Write (nout,*) ' Iterations'
      Write (nout,*)

!     Initial values, root in [0,1].
      x = 0.0_nag_wp
      y = 1.0_nag_wp
      ind = 1
      ifail = -1

!       Reverse communication loop
revcom: Do
        Call c05azf(x,y,fx,tolx,ir,c,ind,ifail)

        If (ind==0) Then
          Exit revcom
        End If

        fx = f(x)
        Write (nout,99999) ' X =', x, '   FX =', fx, '   IND =', ind
      End Do revcom

!     Results
      Select Case (ifail)
      Case (0)
        Write (nout,*)
        Write (nout,*) ' Solution'
        Write (nout,*)
        Write (nout,99998) ' X =', x, '   Y =', y
      Case (4,5)
        Write (nout,99998) 'X =', x, '  Y =', y
      End Select

99999 Format (1X,A,F8.5,A,E12.4,A,I2)
99998 Format (1X,2(A,F8.5))
    End Program c05azfe