program main

c*******************************************************************************
c
cc MAIN is the main program for the F77_SIMPLE example.
c
c  Modified:
c
c    04 December 2006
c
c  Author:
c
c    John Burkardt
c
c  Parameters:
c
c    Local, real A, B, the endpoints of the interval of integration.
c
c    Local, real external F, the name of the function to be integrated.
c
c    Local, integer INT_NUM, the number of intervals to be used.
c
c    Local, real QUAD, the approximate value of the integral.
c
      implicit none

      real a
      real b
      real f
      external f
      integer int_num
      real quad
      integer test

      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'F77_SIMPLE'
      write ( *, '(a)' ) '  A simple FORTRAN77 program to demonstrate'
      write ( *, '(a)' ) '  the use of makefiles.'

      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) '  Estimate the integral from 0 to 1000, of'
      write ( *, '(a)' ) 
     &  '  F(T) = (4+T/365+1/2 sin(pi*T/91)) * (2+exp(-sin(2*pi*T)))'
      write ( *, '(a)' ) 
     &  '  a function which models daily power consumption.'
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 
     &  '  subroutine midpoint ( a, b, f, int_num, quad )'
      write ( *, '(a)' ) 
     &  '  estimates the integral using the midpoint rule.'
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) '  function f ( t )'
      write ( *, '(a)' ) '  evaluates the integrand.'
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) '  Intervals   Estimate'
      write ( *, '(a)' ) ' '

      a = 0.0
      b = 1000.0
      int_num = 100

      do test = 1, 3

        call midpoint ( a, b, f, int_num, quad )

        write ( *, '(2x,i8,2x,g14.6)' ) int_num, quad

        int_num = int_num * 100

      end do
 
      write ( *, '(a)' ) ' '
      write ( *, '(a)' ) 'F77_SIMPLE:'
      write ( *, '(a)' ) '  Normal end of execution.'
 
      stop
      end