#! /usr/bin/env python
#
def cube01_monomial_integral ( e ):

#*****************************************************************************80
#
#% CUBE01_MONOMIAL_INTEGRAL: integrals over the unit cube in 3D.
#
#  Discussion:
#
#    The integration region is 
#
#      0 <= X <= 1,
#      0 <= Y <= 1,
#      0 <= Z <= 1.
#
#    The monomial is F(X,Y,Z) = X^E(1) * Y^E(2) * Z^E(3).
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license. 
#
#  Modified:
#
#    18 January 2014
#
#  Author:
#
#    John Burkardt
#
#  Reference:
#
#    Philip Davis, Philip Rabinowitz,
#    Methods of Numerical Integration,
#    Second Edition,
#    Academic Press, 1984, page 263.
#
#  Parameters:
#
#    Input, integer E(3), the exponents.  Each exponent must be nonnegative.
#
#    Output, real INTEGRAL, the integral.
#
  from sys import exit

  m = 3

  if ( e[0] < 0 or e[1] < 0 or e[2] < 0 ):
    print ( '' )
    print ( 'CUBE01_MONOMIAL_INTEGRAL - Fatal error!' )
    print ( '  All exponents must be nonnegative.' )
    exit ( 'CUBE01_MONOMIAL_INTEGRAL - Fatal error!' )

  integral = 1.0
  for i in range ( 0, m ):
    integral = integral / float ( e[i] + 1 )

  return integral

def cube01_monomial_integral_test ( ):

#*****************************************************************************80
#
#% CUBE01_MONOMIAL_INTEGRAL_TEST tests CUBE01_MONOMIAL_INTEGRAL.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    21 June 2015
#
#  Author:
#
#    John Burkardt
#
  import numpy as np
  import platform
  from cube01_sample import cube01_sample
  from cube01_volume import cube01_volume
  from i4vec_uniform_ab import i4vec_uniform_ab
  from monomial_value import monomial_value

  m = 3
  n = 4192
  test_num = 20

  print ( '' )
  print ( 'CUBE01_MONOMIAL_INTEGRAL_TEST' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  CUBE01_MONOMIAL_INTEGRAL computes the integral of a monomial' )
  print ( '  within the interior of the unit cube in 3D.' )
  print ( '  Compare with a Monte Carlo estimate.' )
#
#  Get sample points.
#
  seed = 123456789
  x, seed = cube01_sample ( n, seed )

  print ( '' )
  print ( '  Number of sample points used is %d' % ( n ) )
#
#  Randomly choose exponents.
#
  print ( '' )
  print ( '  Ex  Ey  Ez     MC-Estimate           Exact      Error' )
  print ( '' )

  for test in range ( 0, test_num ):

    e, seed = i4vec_uniform_ab ( m, 0, 7, seed )

    value = monomial_value ( m, n, e, x )

    result = cube01_volume ( ) * np.sum ( value ) / float ( n )
    exact = cube01_monomial_integral ( e )
    error = abs ( result - exact )

    print ( '  %2d  %2d  %2d  %14.6g  %14.6g  %10.2g' \
      % ( e[0], e[1], e[2], result, exact, error ) )
#
#  Terminate.
#
  print ( '' )
  print ( 'CUBE01_MONOMIAL_INTEGRAL_TEST:' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  cube01_monomial_integral_test ( )
  timestamp ( )