def lcg ( r, m, a, c ):

## lcg() evaluates the next element of a linear congruential generator.
#
  r = ( ( a * r + c ) % m )

  return r

def lcg_test ( ):

  a = 3
  c = 3

  print ( '' )
  print ( 'lcg_test():' )
  print ( '  Test linear congruential generator of the form' )
  print ( '    r = ( ( ', a, ' * r + ', c, ') mod m )' )
  print ( '  for several values of m.' )
  print ( '' )

  for m in [ 7, 13, 17 ]:
    print ( '  Using modulus m = ', m )

    for i in range ( 0, 20 ):
      if ( i == 0 ):
        r = 5
      else:
        r = lcg ( r, m, a, c )
      print ( '', r, end = '' )

    print ( '' )

  return

if ( __name__ == "__main__" ):
  lcg_test ( )