#! /usr/bin/env python
#
def hyperball01_sample ( m, n, seed ):

#*****************************************************************************80
#
## HYPERBALL01_SAMPLE uniformly samples the unit hyperball in M dimensions.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license. 
#
#  Modified:
#
#    22 June 2015
#
#  Author:
#
#    John Burkardt
#
#  Reference:
#
#    Russell Cheng,
#    Random Variate Generation,
#    in Handbook of Simulation,
#    edited by Jerry Banks,
#    Wiley, 1998, pages 168.
#
#    Reuven Rubinstein,
#    Monte Carlo Optimization, Simulation, and Sensitivity 
#    of Queueing Networks,
#    Krieger, 1992,
#    ISBN: 0894647644,
#    LC: QA298.R79.
#
#  Parameters:
#
#    Input, integer M, the spatial dimension.
#
#    Input, integer N, the number of points.
#
#    Input/output, integer SEED, a seed for the random 
#    number generator.
#
#    Output, real X(M,N), the points.
#
  import numpy as np
  from r8_uniform_01 import r8_uniform_01
  from r8vec_norm import r8vec_norm
  from r8vec_normal_01 import r8vec_normal_01

  x = np.zeros ( [ m, n ] )

  exponent = 1.0 / float ( m )

  for j in range ( 0, n ):
#
#  Fill a vector with normally distributed values.
#
    v, seed = r8vec_normal_01 ( m, seed )
#
#  Compute the length of the vector.
#
    norm = r8vec_norm ( m, v )
#
#  Normalize the vector.
#
    for i in range ( 0, m ):
      v[i] = v[i] / norm
#
#  Now compute a value to map the point ON the sphere INTO the sphere.
#
    r, seed = r8_uniform_01 ( seed )

    for i in range ( 0, m ):
      x[i,j] = r ** exponent * v[i]

  return x, seed

def hyperball01_sample_test ( ):

#*****************************************************************************80
#
## HYPERBALL01_SAMPLE_TEST tests HYPERBALL01_SAMPLE.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    22 June 2015
#
#  Author:
#
#    John Burkardt
#
  import platform
  from r8mat_transpose_print import r8mat_transpose_print

  print ( '' )
  print ( 'HYPERBALL01_SAMPLE_TEST' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  HYPERBALL01_SAMPLE samples the unit hyperball.' )

  m = 3
  n = 10
  seed = 123456789

  x, seed = hyperball01_sample ( m, n, seed )

  r8mat_transpose_print ( m, n, x, '  Sample points in the unit hyperball.' )
#
#  Terminate.
#
  print ( '' )
  print ( 'HYPERBALL01_SAMPLE_TEST' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  hyperball01_sample_test ( )
  timestamp ( )