errors.py

   1 """
   2 Errors that can occur when solving a linear game.
   3 """
   4
   5 from cvxopt import matrix
   6
   7 class GameException(Exception):
   8     """
   9     The base class for all exceptions that can occur during the solution
  10     of a linear game.
  11     """
  12     def pretty_print_dict(self, solution_dict):
  13         """
  14         Return a pretty-printed string representation of a CVXOPT
  15         solution dictionary.
  16         """
  17         result = ''
  18         for (k,v) in solution_dict.items():
  19             if isinstance(v, matrix):
  20                 # Try to display vectors as rows on one line.
  21                 result += '  {:s}: {!s}'.format(k,v.trans())
  22             else:
  23                 result += '  {:s}: {!s}\n'.format(k,v)
  24
  25         return result
  26
  27
  28 class GameUnsolvableException(GameException):
  29     """
  30     Every linear game has a solution (this follows from a general
  31     min-max theorem). If we can't solve the conic program associated
  32     with a linear game, then something is wrong with either the model of
  33     the input.
  34     """
  35     def __init__(self, status, solution, solution_dict):
  36         """
  37         Create a new GameUnsolvableException object.
  38
  39         INPUT:
  40
  41         - ``status`` -- the failure status code returned by CVXOPT.
  42
  43         - ``solution`` -- a Solution object.
  44
  45         - ``solution_dict`` -- the solution dictionary returned from the
  46           cone program.
  47
  48         """
  49         tpl = 'Solution failed with error "{:s}".\n' \
  50               '{!s}\n' \
  51               'CVXOPT returned:\n{!s}'
  52               # TODO: dont convert the solution to a string, we need
  53               # to output the two values as well.
  54         self.message = tpl.format(status,
  55                                   solution,
  56                                   self.pretty_print_dict(solution_dict))