pypol/linexprs.py

   1 import ast
   2 import functools
   3 import numbers
   4 import re
   5
   6 from collections import OrderedDict, defaultdict
   7 from fractions import Fraction, gcd
   8
   9
  10 __all__ = [
  11     'Expression',
  12     'Symbol', 'symbols',
  13     'Constant',
  14 ]
  15
  16
  17 def _polymorphic(func):
  18     @functools.wraps(func)
  19     def wrapper(left, right):
  20         if isinstance(right, Expression):
  21             return func(left, right)
  22         elif isinstance(right, numbers.Rational):
  23             right = Constant(right)
  24             return func(left, right)
  25         return NotImplemented
  26     return wrapper
  27
  28
  29 class Expression:
  30     """
  31     This class implements linear expressions.
  32     """
  33
  34     __slots__ = (
  35         '_coefficients',
  36         '_constant',
  37         '_symbols',
  38         '_dimension',
  39     )
  40
  41     def __new__(cls, coefficients=None, constant=0):
  42         if isinstance(coefficients, str):
  43             if constant:
  44                 raise TypeError('too many arguments')
  45             return Expression.fromstring(coefficients)
  46         if coefficients is None:
  47             return Constant(constant)
  48         if isinstance(coefficients, dict):
  49             coefficients = coefficients.items()
  50         for symbol, coefficient in coefficients:
  51             if not isinstance(symbol, Symbol):
  52                 raise TypeError('symbols must be Symbol instances')
  53         coefficients = [(symbol, coefficient)
  54             for symbol, coefficient in coefficients if coefficient != 0]
  55         if len(coefficients) == 0:
  56             return Constant(constant)
  57         if len(coefficients) == 1 and constant == 0:
  58             symbol, coefficient = coefficients[0]
  59             if coefficient == 1:
  60                 return symbol
  61         self = object().__new__(cls)
  62         self._coefficients = OrderedDict()
  63         for symbol, coefficient in sorted(coefficients,
  64                 key=lambda item: item[0].name):
  65             if isinstance(coefficient, Constant):
  66                 coefficient = coefficient.constant
  67             if not isinstance(coefficient, numbers.Rational):
  68                 raise TypeError('coefficients must be rational numbers '
  69                     'or Constant instances')
  70             self._coefficients[symbol] = coefficient
  71         if isinstance(constant, Constant):
  72             constant = constant.constant
  73         if not isinstance(constant, numbers.Rational):
  74             raise TypeError('constant must be a rational number '
  75                 'or a Constant instance')
  76         self._constant = constant
  77         self._symbols = tuple(self._coefficients)
  78         self._dimension = len(self._symbols)
  79         return self
  80
  81     def coefficient(self, symbol):
  82         if not isinstance(symbol, Symbol):
  83             raise TypeError('symbol must be a Symbol instance')
  84         try:
  85             return self._coefficients[symbol]
  86         except KeyError:
  87             return 0
  88
  89     __getitem__ = coefficient
  90
  91     def coefficients(self):
  92         yield from self._coefficients.items()
  93
  94     @property
  95     def constant(self):
  96         return self._constant
  97
  98     @property
  99     def symbols(self):
 100         return self._symbols
 101
 102     @property
 103     def dimension(self):
 104         return self._dimension
 105
 106     def __hash__(self):
 107         return hash((tuple(self._coefficients.items()), self._constant))
 108
 109     def isconstant(self):
 110         return False
 111
 112     def issymbol(self):
 113         return False
 114
 115     def values(self):
 116         yield from self._coefficients.values()
 117         yield self.constant
 118
 119     def __bool__(self):
 120         return True
 121
 122     def __pos__(self):
 123         return self
 124
 125     def __neg__(self):
 126         return self * -1
 127
 128     @_polymorphic
 129     def __add__(self, other):
 130         coefficients = defaultdict(Constant, self.coefficients())
 131         for symbol, coefficient in other.coefficients():
 132             coefficients[symbol] += coefficient
 133         constant = self.constant + other.constant
 134         return Expression(coefficients, constant)
 135
 136     __radd__ = __add__
 137
 138     @_polymorphic
 139     def __sub__(self, other):
 140         coefficients = defaultdict(Constant, self.coefficients())
 141         for symbol, coefficient in other.coefficients():
 142             coefficients[symbol] -= coefficient
 143         constant = self.constant - other.constant
 144         return Expression(coefficients, constant)
 145
 146     def __rsub__(self, other):
 147         return -(self - other)
 148
 149     @_polymorphic
 150     def __mul__(self, other):
 151         if other.isconstant():
 152             coefficients = dict(self.coefficients())
 153             for symbol in coefficients:
 154                 coefficients[symbol] *= other.constant
 155             constant = self.constant * other.constant
 156             return Expression(coefficients, constant)
 157         if isinstance(other, Expression) and not self.isconstant():
 158             raise ValueError('non-linear expression: '
 159                     '{} * {}'.format(self._parenstr(), other._parenstr()))
 160         return NotImplemented
 161
 162     __rmul__ = __mul__
 163
 164     @_polymorphic
 165     def __truediv__(self, other):
 166         if other.isconstant():
 167             coefficients = dict(self.coefficients())
 168             for symbol in coefficients:
 169                 coefficients[symbol] = Constant(coefficients[symbol], other.constant)
 170             constant = Constant(self.constant, other.constant)
 171             return Expression(coefficients, constant)
 172         if isinstance(other, Expression):
 173             raise ValueError('non-linear expression: '
 174                 '{} / {}'.format(self._parenstr(), other._parenstr()))
 175         return NotImplemented
 176
 177     def __rtruediv__(self, other):
 178         if isinstance(other, self):
 179             if self.isconstant():
 180                 return Constant(other, self.constant)
 181             else:
 182                 raise ValueError('non-linear expression: '
 183                         '{} / {}'.format(other._parenstr(), self._parenstr()))
 184         return NotImplemented
 185
 186     @_polymorphic
 187     def __eq__(self, other):
 188         # "normal" equality
 189         # see http://docs.sympy.org/dev/tutorial/gotchas.html#equals-signs
 190         return isinstance(other, Expression) and \
 191             self._coefficients == other._coefficients and \
 192             self.constant == other.constant
 193
 194     @_polymorphic
 195     def __le__(self, other):
 196         from .polyhedra import Le
 197         return Le(self, other)
 198
 199     @_polymorphic
 200     def __lt__(self, other):
 201         from .polyhedra import Lt
 202         return Lt(self, other)
 203
 204     @_polymorphic
 205     def __ge__(self, other):
 206         from .polyhedra import Ge
 207         return Ge(self, other)
 208
 209     @_polymorphic
 210     def __gt__(self, other):
 211         from .polyhedra import Gt
 212         return Gt(self, other)
 213
 214     def scaleint(self):
 215         lcm = functools.reduce(lambda a, b: a*b // gcd(a, b),
 216             [value.denominator for value in self.values()])
 217         return self * lcm
 218
 219     def subs(self, symbol, expression=None):
 220         if expression is None:
 221             if isinstance(symbol, dict):
 222                 symbol = symbol.items()
 223             substitutions = symbol
 224         else:
 225             substitutions = [(symbol, expression)]
 226         result = self
 227         for symbol, expression in substitutions:
 228             coefficients = [(othersymbol, coefficient)
 229                 for othersymbol, coefficient in result.coefficients()
 230                 if othersymbol != symbol]
 231             coefficient = result.coefficient(symbol)
 232             constant = result.constant
 233             result = Expression(coefficients, constant) + coefficient*expression
 234         return result
 235
 236     @classmethod
 237     def _fromast(cls, node):
 238         if isinstance(node, ast.Module) and len(node.body) == 1:
 239             return cls._fromast(node.body[0])
 240         elif isinstance(node, ast.Expr):
 241             return cls._fromast(node.value)
 242         elif isinstance(node, ast.Name):
 243             return Symbol(node.id)
 244         elif isinstance(node, ast.Num):
 245             return Constant(node.n)
 246         elif isinstance(node, ast.UnaryOp) and isinstance(node.op, ast.USub):
 247             return -cls._fromast(node.operand)
 248         elif isinstance(node, ast.BinOp):
 249             left = cls._fromast(node.left)
 250             right = cls._fromast(node.right)
 251             if isinstance(node.op, ast.Add):
 252                 return left + right
 253             elif isinstance(node.op, ast.Sub):
 254                 return left - right
 255             elif isinstance(node.op, ast.Mult):
 256                 return left * right
 257             elif isinstance(node.op, ast.Div):
 258                 return left / right
 259         raise SyntaxError('invalid syntax')
 260
 261     _RE_NUM_VAR = re.compile(r'(\d+|\))\s*([^\W\d_]\w*|\()')
 262
 263     @classmethod
 264     def fromstring(cls, string):
 265         # add implicit multiplication operators, e.g. '5x' -> '5*x'
 266         string = Expression._RE_NUM_VAR.sub(r'\1*\2', string)
 267         tree = ast.parse(string, 'eval')
 268         return cls._fromast(tree)
 269
 270     def __repr__(self):
 271         string = ''
 272         i = 0
 273         for symbol in self.symbols:
 274             coefficient = self.coefficient(symbol)
 275             if coefficient == 1:
 276                 if i == 0:
 277                     string += symbol.name
 278                 else:
 279                     string += ' + {}'.format(symbol)
 280             elif coefficient == -1:
 281                 if i == 0:
 282                     string += '-{}'.format(symbol)
 283                 else:
 284                     string += ' - {}'.format(symbol)
 285             else:
 286                 if i == 0:
 287                     string += '{}*{}'.format(coefficient, symbol)
 288                 elif coefficient > 0:
 289                     string += ' + {}*{}'.format(coefficient, symbol)
 290                 else:
 291                     assert coefficient < 0
 292                     coefficient *= -1
 293                     string += ' - {}*{}'.format(coefficient, symbol)
 294             i += 1
 295         constant = self.constant
 296         if constant != 0 and i == 0:
 297             string += '{}'.format(constant)
 298         elif constant > 0:
 299             string += ' + {}'.format(constant)
 300         elif constant < 0:
 301             constant *= -1
 302             string += ' - {}'.format(constant)
 303         if string == '':
 304             string = '0'
 305         return string
 306
 307     def _parenstr(self, always=False):
 308         string = str(self)
 309         if not always and (self.isconstant() or self.issymbol()):
 310             return string
 311         else:
 312             return '({})'.format(string)
 313
 314     @classmethod
 315     def fromsympy(cls, expr):
 316         import sympy
 317         coefficients = []
 318         constant = 0
 319         for symbol, coefficient in expr.as_coefficients_dict().items():
 320             coefficient = Fraction(coefficient.p, coefficient.q)
 321             if symbol == sympy.S.One:
 322                 constant = coefficient
 323             elif isinstance(symbol, sympy.Symbol):
 324                 symbol = Symbol(symbol.name)
 325                 coefficients.append((symbol, coefficient))
 326             else:
 327                 raise ValueError('non-linear expression: {!r}'.format(expr))
 328         return Expression(coefficients, constant)
 329
 330     def tosympy(self):
 331         import sympy
 332         expr = 0
 333         for symbol, coefficient in self.coefficients():
 334             term = coefficient * sympy.Symbol(symbol.name)
 335             expr += term
 336         expr += self.constant
 337         return expr
 338
 339
 340 class Symbol(Expression):
 341
 342     __slots__ = (
 343         '_name',
 344     )
 345
 346     def __new__(cls, name):
 347         if not isinstance(name, str):
 348             raise TypeError('name must be a string')
 349         self = object().__new__(cls)
 350         self._name = name.strip()
 351         return self
 352
 353     @property
 354     def name(self):
 355         return self._name
 356
 357     def __hash__(self):
 358         return hash(self._name)
 359
 360     def coefficient(self, symbol):
 361         if not isinstance(symbol, Symbol):
 362             raise TypeError('symbol must be a Symbol instance')
 363         if symbol == self:
 364             return 1
 365         else:
 366             return 0
 367
 368     def coefficients(self):
 369         yield self, 1
 370
 371     @property
 372     def constant(self):
 373         return 0
 374
 375     @property
 376     def symbols(self):
 377         return self,
 378
 379     @property
 380     def dimension(self):
 381         return 1
 382
 383     def issymbol(self):
 384         return True
 385
 386     def values(self):
 387         yield 1
 388
 389     def __eq__(self, other):
 390         return isinstance(other, Symbol) and self.name == other.name
 391
 392     @classmethod
 393     def _fromast(cls, node):
 394         if isinstance(node, ast.Module) and len(node.body) == 1:
 395             return cls._fromast(node.body[0])
 396         elif isinstance(node, ast.Expr):
 397             return cls._fromast(node.value)
 398         elif isinstance(node, ast.Name):
 399             return Symbol(node.id)
 400         raise SyntaxError('invalid syntax')
 401
 402     @classmethod
 403     def fromsympy(cls, expr):
 404         import sympy
 405         if isinstance(expr, sympy.Symbol):
 406             return Symbol(expr.name)
 407         else:
 408             raise TypeError('expr must be a sympy.Symbol instance')
 409
 410
 411 def symbols(names):
 412     if isinstance(names, str):
 413         names = names.replace(',', ' ').split()
 414     return tuple(Symbol(name) for name in names)
 415
 416
 417 class Constant(Expression):
 418
 419     __slots__ = (
 420         '_constant',
 421     )
 422
 423     def __new__(cls, numerator=0, denominator=None):
 424         self = object().__new__(cls)
 425         if denominator is None and isinstance(numerator, Constant):
 426             self._constant = numerator.constant
 427         else:
 428             self._constant = Fraction(numerator, denominator)
 429         return self
 430
 431     def __hash__(self):
 432         return hash(self.constant)
 433
 434     def coefficient(self, symbol):
 435         if not isinstance(symbol, Symbol):
 436             raise TypeError('symbol must be a Symbol instance')
 437         return 0
 438
 439     def coefficients(self):
 440         yield from ()
 441
 442     @property
 443     def symbols(self):
 444         return ()
 445
 446     @property
 447     def dimension(self):
 448         return 0
 449
 450     def isconstant(self):
 451         return True
 452
 453     def values(self):
 454         yield self._constant
 455
 456     @_polymorphic
 457     def __eq__(self, other):
 458         return isinstance(other, Constant) and self.constant == other.constant
 459
 460     def __bool__(self):
 461         return self.constant != 0
 462
 463     @classmethod
 464     def fromstring(cls, string):
 465         if not isinstance(string, str):
 466             raise TypeError('string must be a string instance')
 467         return Constant(Fraction(string))
 468
 469     @classmethod
 470     def fromsympy(cls, expr):
 471         import sympy
 472         if isinstance(expr, sympy.Rational):
 473             return Constant(expr.p, expr.q)
 474         elif isinstance(expr, numbers.Rational):
 475             return Constant(expr)
 476         else:
 477             raise TypeError('expr must be a sympy.Rational instance')