linpy/linexprs.py

   1 # Copyright 2014 MINES ParisTech
   2 #
   3 # This file is part of LinPy.
   4 #
   5 # LinPy is free software: you can redistribute it and/or modify
   6 # it under the terms of the GNU General Public License as published by
   7 # the Free Software Foundation, either version 3 of the License, or
   8 # (at your option) any later version.
   9 #
  10 # LinPy is distributed in the hope that it will be useful,
  11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 # GNU General Public License for more details.
  14 #
  15 # You should have received a copy of the GNU General Public License
  16 # along with LinPy.  If not, see <http://www.gnu.org/licenses/>.
  17
  18 import ast
  19 import functools
  20 import numbers
  21 import re
  22
  23 from collections import OrderedDict, defaultdict, Mapping
  24 from fractions import Fraction, gcd
  25
  26
  27 __all__ = [
  28     'Expression',
  29     'Symbol', 'Dummy', 'symbols',
  30     'Rational',
  31 ]
  32
  33
  34 def _polymorphic(func):
  35     @functools.wraps(func)
  36     def wrapper(left, right):
  37         if isinstance(right, Expression):
  38             return func(left, right)
  39         elif isinstance(right, numbers.Rational):
  40             right = Rational(right)
  41             return func(left, right)
  42         return NotImplemented
  43     return wrapper
  44
  45
  46 class Expression:
  47     """
  48     This class implements linear expressions.
  49     """
  50
  51     def __new__(cls, coefficients=None, constant=0):
  52         if isinstance(coefficients, str):
  53             if constant != 0:
  54                 raise TypeError('too many arguments')
  55             return Expression.fromstring(coefficients)
  56         if coefficients is None:
  57             return Rational(constant)
  58         if isinstance(coefficients, Mapping):
  59             coefficients = coefficients.items()
  60         coefficients = list(coefficients)
  61         for symbol, coefficient in coefficients:
  62             if not isinstance(symbol, Symbol):
  63                 raise TypeError('symbols must be Symbol instances')
  64             if not isinstance(coefficient, numbers.Rational):
  65                 raise TypeError('coefficients must be rational numbers')
  66         if not isinstance(constant, numbers.Rational):
  67             raise TypeError('constant must be a rational number')
  68         if len(coefficients) == 0:
  69             return Rational(constant)
  70         if len(coefficients) == 1 and constant == 0:
  71             symbol, coefficient = coefficients[0]
  72             if coefficient == 1:
  73                 return symbol
  74         coefficients = [(symbol, Fraction(coefficient))
  75             for symbol, coefficient in coefficients if coefficient != 0]
  76         coefficients.sort(key=lambda item: item[0].sortkey())
  77         self = object().__new__(cls)
  78         self._coefficients = OrderedDict(coefficients)
  79         self._constant = Fraction(constant)
  80         self._symbols = tuple(self._coefficients)
  81         self._dimension = len(self._symbols)
  82         return self
  83
  84     def coefficient(self, symbol):
  85         if not isinstance(symbol, Symbol):
  86             raise TypeError('symbol must be a Symbol instance')
  87         return Rational(self._coefficients.get(symbol, 0))
  88
  89     __getitem__ = coefficient
  90
  91     def coefficients(self):
  92         for symbol, coefficient in self._coefficients.items():
  93             yield symbol, Rational(coefficient)
  94
  95     @property
  96     def constant(self):
  97         return Rational(self._constant)
  98
  99     @property
 100     def symbols(self):
 101         return self._symbols
 102
 103     @property
 104     def dimension(self):
 105         return self._dimension
 106
 107     def __hash__(self):
 108         return hash((tuple(self._coefficients.items()), self._constant))
 109
 110     def isconstant(self):
 111         return False
 112
 113     def issymbol(self):
 114         return False
 115
 116     def values(self):
 117         for coefficient in self._coefficients.values():
 118             yield Rational(coefficient)
 119         yield Rational(self._constant)
 120
 121     def __bool__(self):
 122         return True
 123
 124     def __pos__(self):
 125         return self
 126
 127     def __neg__(self):
 128         return self * -1
 129
 130     @_polymorphic
 131     def __add__(self, other):
 132         coefficients = defaultdict(Fraction, self._coefficients)
 133         for symbol, coefficient in other._coefficients.items():
 134             coefficients[symbol] += coefficient
 135         constant = self._constant + other._constant
 136         return Expression(coefficients, constant)
 137
 138     __radd__ = __add__
 139
 140     @_polymorphic
 141     def __sub__(self, other):
 142         coefficients = defaultdict(Fraction, self._coefficients)
 143         for symbol, coefficient in other._coefficients.items():
 144             coefficients[symbol] -= coefficient
 145         constant = self._constant - other._constant
 146         return Expression(coefficients, constant)
 147
 148     @_polymorphic
 149     def __rsub__(self, other):
 150         return other - self
 151
 152     def __mul__(self, other):
 153         if isinstance(other, numbers.Rational):
 154             coefficients = ((symbol, coefficient * other)
 155                 for symbol, coefficient in self._coefficients.items())
 156             constant = self._constant * other
 157             return Expression(coefficients, constant)
 158         return NotImplemented
 159
 160     __rmul__ = __mul__
 161
 162     def __truediv__(self, other):
 163         if isinstance(other, numbers.Rational):
 164             coefficients = ((symbol, coefficient / other)
 165                 for symbol, coefficient in self._coefficients.items())
 166             constant = self._constant / other
 167             return Expression(coefficients, constant)
 168         return NotImplemented
 169
 170     @_polymorphic
 171     def __eq__(self, other):
 172         # returns a boolean, not a constraint
 173         # see http://docs.sympy.org/dev/tutorial/gotchas.html#equals-signs
 174         return isinstance(other, Expression) and \
 175             self._coefficients == other._coefficients and \
 176             self._constant == other._constant
 177
 178     def __le__(self, other):
 179         from .polyhedra import Le
 180         return Le(self, other)
 181
 182     def __lt__(self, other):
 183         from .polyhedra import Lt
 184         return Lt(self, other)
 185
 186     def __ge__(self, other):
 187         from .polyhedra import Ge
 188         return Ge(self, other)
 189
 190     def __gt__(self, other):
 191         from .polyhedra import Gt
 192         return Gt(self, other)
 193
 194     def scaleint(self):
 195         lcm = functools.reduce(lambda a, b: a*b // gcd(a, b),
 196             [value.denominator for value in self.values()])
 197         return self * lcm
 198
 199     def subs(self, symbol, expression=None):
 200         if expression is None:
 201             if isinstance(symbol, Mapping):
 202                 symbol = symbol.items()
 203             substitutions = symbol
 204         else:
 205             substitutions = [(symbol, expression)]
 206         result = self
 207         for symbol, expression in substitutions:
 208             if not isinstance(symbol, Symbol):
 209                 raise TypeError('symbols must be Symbol instances')
 210             coefficients = [(othersymbol, coefficient)
 211                 for othersymbol, coefficient in result._coefficients.items()
 212                 if othersymbol != symbol]
 213             coefficient = result._coefficients.get(symbol, 0)
 214             constant = result._constant
 215             result = Expression(coefficients, constant) + coefficient*expression
 216         return result
 217
 218     @classmethod
 219     def _fromast(cls, node):
 220         if isinstance(node, ast.Module) and len(node.body) == 1:
 221             return cls._fromast(node.body[0])
 222         elif isinstance(node, ast.Expr):
 223             return cls._fromast(node.value)
 224         elif isinstance(node, ast.Name):
 225             return Symbol(node.id)
 226         elif isinstance(node, ast.Num):
 227             return Rational(node.n)
 228         elif isinstance(node, ast.UnaryOp) and isinstance(node.op, ast.USub):
 229             return -cls._fromast(node.operand)
 230         elif isinstance(node, ast.BinOp):
 231             left = cls._fromast(node.left)
 232             right = cls._fromast(node.right)
 233             if isinstance(node.op, ast.Add):
 234                 return left + right
 235             elif isinstance(node.op, ast.Sub):
 236                 return left - right
 237             elif isinstance(node.op, ast.Mult):
 238                 return left * right
 239             elif isinstance(node.op, ast.Div):
 240                 return left / right
 241         raise SyntaxError('invalid syntax')
 242
 243     _RE_NUM_VAR = re.compile(r'(\d+|\))\s*([^\W\d_]\w*|\()')
 244
 245     @classmethod
 246     def fromstring(cls, string):
 247         # add implicit multiplication operators, e.g. '5x' -> '5*x'
 248         string = Expression._RE_NUM_VAR.sub(r'\1*\2', string)
 249         tree = ast.parse(string, 'eval')
 250         return cls._fromast(tree)
 251
 252     def __repr__(self):
 253         string = ''
 254         for i, (symbol, coefficient) in enumerate(self.coefficients()):
 255             if coefficient == 1:
 256                 if i != 0:
 257                     string += ' + '
 258             elif coefficient == -1:
 259                 string += '-' if i == 0 else ' - '
 260             elif i == 0:
 261                 string += '{}*'.format(coefficient)
 262             elif coefficient > 0:
 263                 string += ' + {}*'.format(coefficient)
 264             else:
 265                 string += ' - {}*'.format(-coefficient)
 266             string += '{}'.format(symbol)
 267         constant = self.constant
 268         if len(string) == 0:
 269             string += '{}'.format(constant)
 270         elif constant > 0:
 271             string += ' + {}'.format(constant)
 272         elif constant < 0:
 273             string += ' - {}'.format(-constant)
 274         return string
 275
 276     def _repr_latex_(self):
 277         string = ''
 278         for i, (symbol, coefficient) in enumerate(self.coefficients()):
 279             if coefficient == 1:
 280                 if i != 0:
 281                     string += ' + '
 282             elif coefficient == -1:
 283                 string += '-' if i == 0 else ' - '
 284             elif i == 0:
 285                 string += '{}'.format(coefficient._repr_latex_().strip('$'))
 286             elif coefficient > 0:
 287                 string += ' + {}'.format(coefficient._repr_latex_().strip('$'))
 288             elif coefficient < 0:
 289                 string += ' - {}'.format((-coefficient)._repr_latex_().strip('$'))
 290             string += '{}'.format(symbol._repr_latex_().strip('$'))
 291         constant = self.constant
 292         if len(string) == 0:
 293             string += '{}'.format(constant._repr_latex_().strip('$'))
 294         elif constant > 0:
 295             string += ' + {}'.format(constant._repr_latex_().strip('$'))
 296         elif constant < 0:
 297             string += ' - {}'.format((-constant)._repr_latex_().strip('$'))
 298         return '$${}$$'.format(string)
 299
 300     def _parenstr(self, always=False):
 301         string = str(self)
 302         if not always and (self.isconstant() or self.issymbol()):
 303             return string
 304         else:
 305             return '({})'.format(string)
 306
 307     @classmethod
 308     def fromsympy(cls, expr):
 309         import sympy
 310         coefficients = []
 311         constant = 0
 312         for symbol, coefficient in expr.as_coefficients_dict().items():
 313             coefficient = Fraction(coefficient.p, coefficient.q)
 314             if symbol == sympy.S.One:
 315                 constant = coefficient
 316             elif isinstance(symbol, sympy.Symbol):
 317                 symbol = Symbol(symbol.name)
 318                 coefficients.append((symbol, coefficient))
 319             else:
 320                 raise ValueError('non-linear expression: {!r}'.format(expr))
 321         return Expression(coefficients, constant)
 322
 323     def tosympy(self):
 324         import sympy
 325         expr = 0
 326         for symbol, coefficient in self.coefficients():
 327             term = coefficient * sympy.Symbol(symbol.name)
 328             expr += term
 329         expr += self.constant
 330         return expr
 331
 332
 333 class Symbol(Expression):
 334
 335     def __new__(cls, name):
 336         if not isinstance(name, str):
 337             raise TypeError('name must be a string')
 338         self = object().__new__(cls)
 339         self._name = name.strip()
 340         self._coefficients = {self: Fraction(1)}
 341         self._constant = Fraction(0)
 342         self._symbols = (self,)
 343         self._dimension = 1
 344         return self
 345
 346     @property
 347     def name(self):
 348         return self._name
 349
 350     def __hash__(self):
 351         return hash(self.sortkey())
 352
 353     def sortkey(self):
 354         return self.name,
 355
 356     def issymbol(self):
 357         return True
 358
 359     def __eq__(self, other):
 360         return self.sortkey() == other.sortkey()
 361
 362     def asdummy(self):
 363         return Dummy(self.name)
 364
 365     @classmethod
 366     def _fromast(cls, node):
 367         if isinstance(node, ast.Module) and len(node.body) == 1:
 368             return cls._fromast(node.body[0])
 369         elif isinstance(node, ast.Expr):
 370             return cls._fromast(node.value)
 371         elif isinstance(node, ast.Name):
 372             return Symbol(node.id)
 373         raise SyntaxError('invalid syntax')
 374
 375     def __repr__(self):
 376         return self.name
 377
 378     def _repr_latex_(self):
 379         return '$${}$$'.format(self.name)
 380
 381     @classmethod
 382     def fromsympy(cls, expr):
 383         import sympy
 384         if isinstance(expr, sympy.Dummy):
 385             return Dummy(expr.name)
 386         elif isinstance(expr, sympy.Symbol):
 387             return Symbol(expr.name)
 388         else:
 389             raise TypeError('expr must be a sympy.Symbol instance')
 390
 391
 392 class Dummy(Symbol):
 393
 394     _count = 0
 395
 396     def __new__(cls, name=None):
 397         if name is None:
 398             name = 'Dummy_{}'.format(Dummy._count)
 399         elif not isinstance(name, str):
 400             raise TypeError('name must be a string')
 401         self = object().__new__(cls)
 402         self._index = Dummy._count
 403         self._name = name.strip()
 404         self._coefficients = {self: Fraction(1)}
 405         self._constant = Fraction(0)
 406         self._symbols = (self,)
 407         self._dimension = 1
 408         Dummy._count += 1
 409         return self
 410
 411     def __hash__(self):
 412         return hash(self.sortkey())
 413
 414     def sortkey(self):
 415         return self._name, self._index
 416
 417     def __repr__(self):
 418         return '_{}'.format(self.name)
 419
 420     def _repr_latex_(self):
 421         return '$${}_{{{}}}$$'.format(self.name, self._index)
 422
 423
 424 def symbols(names):
 425     if isinstance(names, str):
 426         names = names.replace(',', ' ').split()
 427     return tuple(Symbol(name) for name in names)
 428
 429
 430 class Rational(Expression, Fraction):
 431
 432     def __new__(cls, numerator=0, denominator=None):
 433         self = object().__new__(cls)
 434         self._coefficients = {}
 435         self._constant = Fraction(numerator, denominator)
 436         self._symbols = ()
 437         self._dimension = 0
 438         self._numerator = self._constant.numerator
 439         self._denominator = self._constant.denominator
 440         return self
 441
 442     def __hash__(self):
 443         return Fraction.__hash__(self)
 444
 445     @property
 446     def constant(self):
 447         return self
 448
 449     def isconstant(self):
 450         return True
 451
 452     def __bool__(self):
 453         return Fraction.__bool__(self)
 454
 455     def __repr__(self):
 456         if self.denominator == 1:
 457             return '{!r}'.format(self.numerator)
 458         else:
 459             return '{!r}/{!r}'.format(self.numerator, self.denominator)
 460
 461     def _repr_latex_(self):
 462         if self.denominator == 1:
 463             return '$${}$$'.format(self.numerator)
 464         elif self.numerator < 0:
 465             return '$$-\\frac{{{}}}{{{}}}$$'.format(-self.numerator,
 466                 self.denominator)
 467         else:
 468             return '$$\\frac{{{}}}{{{}}}$$'.format(self.numerator,
 469                 self.denominator)
 470
 471     @classmethod
 472     def fromsympy(cls, expr):
 473         import sympy
 474         if isinstance(expr, sympy.Rational):
 475             return Rational(expr.p, expr.q)
 476         elif isinstance(expr, numbers.Rational):
 477             return Rational(expr)
 478         else:
 479             raise TypeError('expr must be a sympy.Rational instance')