#! /usr/bin/env python
#
def r8_log_b ( x, b ):

#*****************************************************************************80
#
## R8_LOG_B returns the logarithm base B of |X|.
#
#  Discussion:
#
#    value = log ( |X| ) / log ( |B| )
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license. 
#
#  Modified:
#
#    09 October 2016
#
#  Author:
#
#    John Burkardt
#
#  Parameters:
#
#    Input, real X, the number whose base B logarithm is desired.
#    X should not be 0.
#
#    Input, real B, the base, which should not be 0, 1 or -1.
#
#    Output, real VALUE, the logarithm base B of the absolute
#    value of X.  It should be true that |X| = |B|^D_LOG_B.
#
  import numpy as np

  value = np.log ( abs ( x ) ) / np.log ( abs ( b ) )

  return value

def r8_log_b_test ( ):

#*****************************************************************************80
#
## R8_LOG_B_TEST tests R8_LOG_B.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    25 July 2014
#
#  Author:
#
#    John Burkardt
#
  import numpy as np
  import platform

  test_num = 10

  b_test = np.array ( [ \
    2.0, 3.0, 4.0, 5.0, 6.0, \
    7.0, 8.0, 16.0, 32.0, 256.0 ] )

  x = 16.0

  print ( '' )
  print ( 'R8_LOG_B_TEST' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  R8_LOG_B computes the logarithm base B.' )
  print ( '' )
  print ( '        X             B             R8_LOG_B' )
  print ( '' )

  for test in range ( 0, test_num ):

    b = b_test[test]

    print ( '  %12f  %12f  %12f' % ( x, b, r8_log_b ( x, b ) ) )
#
#  Terminate.
#
  print ( '' )
  print ( 'R8_LOG_B_TEST' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  r8_log_b_test ( )
  timestamp ( )