X-Git-Url: https://scm.cri.ensmp.fr/git/linpy.git/blobdiff_plain/538cd0d05962f48885e8dd68c93a0a1af67b9607..b2931230a184025bdb6006bfe48c9b1dc18dc351:/linpy/linexprs.py diff --git a/linpy/linexprs.py b/linpy/linexprs.py index c100698..eff4a7e 100644 --- a/linpy/linexprs.py +++ b/linpy/linexprs.py @@ -62,7 +62,7 @@ class LinExpr: symbols to their coefficients, and a constant term. The coefficients and the constant term must be rational numbers. - For example, the linear expression x + 2y + 1 can be constructed using + For example, the linear expression x + 2*y + 1 can be constructed using one of the following instructions: >>> x, y = symbols('x y') @@ -76,7 +76,7 @@ class LinExpr: Alternatively, linear expressions can be constructed from a string: - >>> LinExpr('x + 2*y + 1') + >>> LinExpr('x + 2y + 1') A linear expression with a single symbol of coefficient 1 and no constant term is automatically subclassed as a Symbol instance. A linear @@ -245,28 +245,34 @@ class LinExpr: @_polymorphic def __eq__(self, other): """ - Test whether two linear expressions are equal. + Test whether two linear expressions are equal. Unlike methods + LinExpr.__lt__(), LinExpr.__le__(), LinExpr.__ge__(), LinExpr.__gt__(), + the result is a boolean value, not a polyhedron. To express that two + linear expressions are equal or not equal, use functions Eq() and Ne() + instead. """ - if isinstance(other, LinExpr): - return self._coefficients == other._coefficients and \ - self._constant == other._constant - return NotImplemented - - def __le__(self, other): - from .polyhedra import Le - return Le(self, other) + return self._coefficients == other._coefficients and \ + self._constant == other._constant + @_polymorphic def __lt__(self, other): - from .polyhedra import Lt - return Lt(self, other) + from .polyhedra import Polyhedron + return Polyhedron([], [other - self - 1]) + @_polymorphic + def __le__(self, other): + from .polyhedra import Polyhedron + return Polyhedron([], [other - self]) + + @_polymorphic def __ge__(self, other): - from .polyhedra import Ge - return Ge(self, other) + from .polyhedra import Polyhedron + return Polyhedron([], [self - other]) + @_polymorphic def __gt__(self, other): - from .polyhedra import Gt - return Gt(self, other) + from .polyhedra import Polyhedron + return Polyhedron([], [self - other - 1]) def scaleint(self): """ @@ -339,7 +345,7 @@ class LinExpr: Create an expression from a string. Raise SyntaxError if the string is not properly formatted. """ - # add implicit multiplication operators, e.g. '5x' -> '5*x' + # Add implicit multiplication operators, e.g. '5x' -> '5*x'. string = LinExpr._RE_NUM_VAR.sub(r'\1*\2', string) tree = ast.parse(string, 'eval') expr = cls._fromast(tree) @@ -405,7 +411,7 @@ class LinExpr: @classmethod def fromsympy(cls, expr): """ - Create a linear expression from a sympy expression. Raise TypeError is + Create a linear expression from a SymPy expression. Raise TypeError is the sympy expression is not linear. """ import sympy @@ -416,7 +422,8 @@ class LinExpr: if symbol == sympy.S.One: constant = coefficient elif isinstance(symbol, sympy.Dummy): - # we cannot properly convert dummy symbols + # We cannot properly convert dummy symbols with respect to + # symbol equalities. raise TypeError('cannot convert dummy symbols') elif isinstance(symbol, sympy.Symbol): symbol = Symbol(symbol.name) @@ -430,7 +437,7 @@ class LinExpr: def tosympy(self): """ - Convert the linear expression to a sympy expression. + Convert the linear expression to a SymPy expression. """ import sympy expr = 0 @@ -477,6 +484,8 @@ class Symbol(LinExpr): @property def _coefficients(self): + # This is not implemented as an attribute, because __hash__ is not + # callable in __new__ in class Dummy. return {self: Fraction(1)} @property