program main

c*********************************************************************72
c
cc zero_chandrupatla_test() tests zero_chandrupatla().
c
c  Licensing:
c
c    This code is distributed under the MIT license.
c
c  Modified:
c
c    19 March 2024
c
c  Author:
c
c    John Burkardt
c
      implicit none

      double precision a
      double precision b
      double precision, external :: f_01
      double precision, external :: f_02
      double precision, external :: f_03
      double precision, external :: f_04
      double precision, external :: f_05
      double precision, external :: f_06
      double precision, external :: f_07
      double precision, external :: f_08
      double precision, external :: f_09
      character ( len = 100 ) title

      call timestamp ( )
      write ( *, '(a)' ) ''
      write ( *, '(a)' ) 'zero_chandrupatla_test():'
      write ( *, '(a)' ) '  Fortran77 version'
      write ( *, '(a)' ) '  zero_chandrupatla() seeks a root of a'
      write ( *, '(a)' ) '  function f(x) in an interval [a,b].'

      a = 2.0
      b = 3.0
      title = 'f_01(x) = x**3 - 2 x - 5'
      call zero_chandrupatla_example ( f_01, a, b, title )

      a = 0.5
      b = 1.51
      title = 'f_02(x) = 1 - 1/x**2'
      call zero_chandrupatla_example ( f_02, a, b, title )

      a = 0.0
      b = 5.0
      title = 'f_03(x) = ( x - 3 )**3'
      call zero_chandrupatla_example ( f_03, a, b, title )

      a = 0.0
      b = 5.0
      title = 'f_04(x) = 6 * ( x - 2 )**5'
      call zero_chandrupatla_example ( f_04, a, b, title )

      a = -1.0
      b = 4.0
      title = 'f_05(x) = x**9'
      call zero_chandrupatla_example ( f_05, a, b, title )

      a = -1.0
      b = 4.0
      title = 'f_06(x) = x**19'
      call zero_chandrupatla_example ( f_06, a, b, title )

      a = -1.0
      b = 4.0
      title = 'f_07(x) = x e**(-1/x2)'
      call zero_chandrupatla_example ( f_07, a, b, title )

      a = 0.0002
      b = 2.0
      title = 'f_08(x) = ' //
     &  '-(3062(1-xi)e**(-x)/(xi+(1-xi)e**(-x)) - 1013 + 1628/x'
      call zero_chandrupatla_example ( f_08, a, b, title )

      a = 0.0002
      b = 1.0
      title = 'f_09(x) = e**x - 2 - 0.01/x**2 + 0.000002/x**3'
      call zero_chandrupatla_example ( f_09, a, b, title )
c
c  Terminate.
c
      write ( *, '(a)' ) ''
      write ( *, '(a)' ) 'zero_chandrupatla_test():'
      write ( *, '(a)' ) '  Normal end of execution.'
      write ( *, '(a)' ) ''
      call timestamp ( )

      return
      end
      subroutine zero_chandrupatla_example ( f, a, b, title )

c*********************************************************************72
c
cc zero_chandrupatla_example() tests zero_chandrupatla() on a test function.
c
c  Licensing:
c
c    This code is distributed under the MIT license.
c
c  Modified:
c
c    19 March 2024
c
c  Author:
c
c    John Burkardt
c
c  Input:
c
c    function f ( x ): the user-supplied function.
c
c    real a, b: the endpoints of the change of sign interval.
c
c    string title: a title for the problem.
c
      implicit none

      double precision a
      double precision b
      integer calls
      double precision, external :: f
      double precision fa
      double precision fb
      double precision fz
      character ( len = * ) title
      double precision z

      call zero_chandrupatla ( f, a, b, z, fz, calls )

      fz = f ( z )
      fa = f ( a )
      fb = f ( b )

      write ( *, '(a)' ) ''
      write ( *, '(2x,a)' ) trim ( title )
      write ( *, '(a)' ) ''
      write ( *, '(a)' ) '      A                 Z             B'
      write ( *, '(a)' ) '    F(A)              F(Z)          F(B)'
      write ( *, '(a)' ) ''
      write ( *, '(2x,f14.6,2x,f14.6,2x,f14.6)' ) a,  z,  b
      write ( *, '(2x,g14.6,2x,g14.6,2x,g14.6)' ) fa, fz, fb
      write ( *, '(a,i4)' ) '  Number of calls to F = ', calls

      return
      end
      function f_01 ( x )

c*********************************************************************72
c
cc f_01() evaluates function 1.
c
      implicit none

      double precision f_01
      double precision x

      f_01 = x**3 - 2.0 * x - 5.0

      return
      end
      function f_02 ( x )

c*********************************************************************72
c
cc f_02() evaluates function 2.
c
      implicit none

      double precision f_02
      double precision x

      f_02 = 1.0 - 1.0 / x**2

      return
      end
      function f_03 ( x )

c*********************************************************************72
c
cc f_03() evaluates function 3.
c
      implicit none

      double precision f_03
      double precision x

      f_03 = ( x - 3.0 )**3

      return
      end
      function f_04 ( x )

c*********************************************************************72
c
cc f_04() evaluates function 4.
c
      implicit none

      double precision f_04
      double precision x

      f_04 = 6.0 * ( x - 2.0 )**5

      return
      end
      function f_05 ( x )

c*********************************************************************72
c
cc f_05() evaluates function 5.
c
      implicit none

      double precision f_05
      double precision x

      f_05 = x**9

      return
      end
      function f_06 ( x )

c*********************************************************************72
c
cc f_06() evaluates function 6.
c
      implicit none

      double precision f_06
      double precision x

      f_06 = x**19

      return
      end
      function f_07 ( x )

c*********************************************************************72
c
cc f_07() evaluates function 7.
c
      implicit none

      double precision f_07
      double precision x

      if ( abs ( x ) < 3.8D-04 ) then
        f_07 = 0.0
      else
        f_07 = x * exp ( - ( 1.0 / x**2 ) )
      end if

      return
      end
      function f_08 ( x )

c*********************************************************************72
c
cc f_08() evaluates function 8.
c
      implicit none

      double precision bot
      double precision f_08
      double precision top
      double precision x
      double precision xi

      xi = 0.61489
      top = ( 3062.0 * ( 1.0 - xi ) * exp ( - x ) )
      bot = ( xi + ( 1.0 - xi ) * exp ( - x ) )

      f_08 = - top / bot - 1013.0 + 1628.0 / x

      return
      end
      function f_09 ( x )

c*********************************************************************72
c
cc f_09() evaluates function 9.
c
      implicit none

      double precision f_09
      double precision x

      f_09 = exp ( x ) - 2.0 - 0.01D+00 / x**2 + 0.000002D+00 / x**3

      return
      end
      subroutine timestamp ( )

c*********************************************************************72
c
cc timestamp() prints the YMDHMS date as a timestamp.
c
c  Licensing:
c
c    This code is distributed under the MIT license.
c
c  Modified:
c
c    12 June 2014
c
c  Author:
c
c    John Burkardt
c
      implicit none

      character * ( 8 ) ampm
      integer d
      character * ( 8 ) date
      integer h
      integer m
      integer mm
      character * ( 9 ) month(12)
      integer n
      integer s
      character * ( 10 ) time
      integer y

      save month

      data month /
     &  'January  ', 'February ', 'March    ', 'April    ', 
     &  'May      ', 'June     ', 'July     ', 'August   ', 
     &  'September', 'October  ', 'November ', 'December ' /

      call date_and_time ( date, time )

      read ( date, '(i4,i2,i2)' ) y, m, d
      read ( time, '(i2,i2,i2,1x,i3)' ) h, n, s, mm

      if ( h .lt. 12 ) then
        ampm = 'AM'
      else if ( h .eq. 12 ) then
        if ( n .eq. 0 .and. s .eq. 0 ) then
          ampm = 'Noon'
        else
          ampm = 'PM'
        end if
      else
        h = h - 12
        if ( h .lt. 12 ) then
          ampm = 'PM'
        else if ( h .eq. 12 ) then
          if ( n .eq. 0 .and. s .eq. 0 ) then
            ampm = 'Midnight'
          else
            ampm = 'AM'
          end if
        end if
      end if

      write ( *, 
     &  '(i2,1x,a,1x,i4,2x,i2,a1,i2.2,a1,i2.2,a1,i3.3,1x,a)' ) 
     &  d, trim ( month(m) ), y, h, ':', n, ':', s, '.', mm, 
     &  trim ( ampm )

      return
      end