from .islhelper import mainctx, libisl
from .geometry import GeometricObject, Point
-from .linexprs import Expression, Rational
+from .linexprs import LinExpr, Rational
from .domains import Domain
class Polyhedron(Domain):
+ """
+ A convex polyhedron (or simply "polyhedron") is the space defined by a
+ system of linear equalities and inequalities. This space can be
+ unbounded.
+ """
__slots__ = (
'_equalities',
)
def __new__(cls, equalities=None, inequalities=None):
+ """
+ Return a polyhedron from two sequences of linear expressions: equalities
+ is a list of expressions equal to 0, and inequalities is a list of
+ expressions greater or equal to 0. For example, the polyhedron
+ 0 <= x <= 2, 0 <= y <= 2 can be constructed with:
+
+ >>> x, y = symbols('x y')
+ >>> square = Polyhedron([], [x, 2 - x, y, 2 - y])
+
+ It may be easier to use comparison operators LinExpr.__lt__(),
+ LinExpr.__le__(), LinExpr.__ge__(), LinExpr.__gt__(), or functions Lt(),
+ Le(), Eq(), Ge() and Gt(), using one of the following instructions:
+
+ >>> x, y = symbols('x y')
+ >>> square = (0 <= x) & (x <= 2) & (0 <= y) & (y <= 2)
+ >>> square = Le(0, x, 2) & Le(0, y, 2)
+
+ It is also possible to build a polyhedron from a string.
+
+ >>> square = Polyhedron('0 <= x <= 2, 0 <= y <= 2')
+
+ Finally, a polyhedron can be constructed from a GeometricObject
+ instance, calling the GeometricObject.aspolyedron() method. This way, it
+ is possible to compute the polyhedral hull of a Domain instance, i.e.,
+ the convex hull of two polyhedra:
+
+ >>> square = Polyhedron('0 <= x <= 2, 0 <= y <= 2')
+ >>> square2 = Polyhedron('2 <= x <= 4, 2 <= y <= 4')
+ >>> Polyhedron(square | square2)
+ """
if isinstance(equalities, str):
if inequalities is not None:
raise TypeError('too many arguments')
equalities = []
else:
for i, equality in enumerate(equalities):
- if not isinstance(equality, Expression):
+ if not isinstance(equality, LinExpr):
raise TypeError('equalities must be linear expressions')
equalities[i] = equality.scaleint()
if inequalities is None:
inequalities = []
else:
for i, inequality in enumerate(inequalities):
- if not isinstance(inequality, Expression):
+ if not isinstance(inequality, LinExpr):
raise TypeError('inequalities must be linear expressions')
inequalities[i] = inequality.scaleint()
symbols = cls._xsymbols(equalities + inequalities)
@property
def equalities(self):
"""
- Return a list of the equalities in a set.
+ The tuple of equalities. This is a list of LinExpr instances that are
+ equal to 0 in the polyhedron.
"""
return self._equalities
@property
def inequalities(self):
"""
- Return a list of the inequalities in a set.
+ The tuple of inequalities. This is a list of LinExpr instances that are
+ greater or equal to 0 in the polyhedron.
"""
return self._inequalities
@property
def constraints(self):
"""
- Return ta list of the constraints of a set.
+ The tuple of constraints, i.e., equalities and inequalities. This is
+ semantically equivalent to: equalities + inequalities.
"""
return self._constraints
def polyhedra(self):
return self,
- def disjoint(self):
- """
- Return a set as disjoint.
- """
+ def make_disjoint(self):
return self
def isuniverse(self):
- """
- Return true if a set is the Universe set.
- """
islbset = self._toislbasicset(self.equalities, self.inequalities,
self.symbols)
universe = bool(libisl.isl_basic_set_is_universe(islbset))
return universe
def aspolyhedron(self):
- """
- Return polyhedral hull of a set.
- """
return self
def __contains__(self, point):
return True
def subs(self, symbol, expression=None):
- """
- Subsitute the given value into an expression and return the resulting
- expression.
- """
equalities = [equality.subs(symbol, expression)
for equality in self.equalities]
inequalities = [inequality.subs(symbol, expression)
return inequalities
def widen(self, other):
+ """
+ Compute the standard widening of two polyhedra, à la Halbwachs.
+ """
if not isinstance(other, Polyhedron):
raise ValueError('argument must be a Polyhedron instance')
inequalities1 = self._asinequalities()
coefficient = islhelper.isl_val_to_int(coefficient)
if coefficient != 0:
coefficients[symbol] = coefficient
- expression = Expression(coefficients, constant)
+ expression = LinExpr(coefficients, constant)
if libisl.isl_constraint_is_equality(islconstraint):
equalities.append(expression)
else:
else:
return 'And({})'.format(', '.join(strings))
-
def _repr_latex_(self):
strings = []
for equality in self.equalities:
@classmethod
def fromsympy(cls, expr):
- """
- Convert a sympy object to an expression.
- """
domain = Domain.fromsympy(expr)
if not isinstance(domain, Polyhedron):
raise ValueError('non-polyhedral expression: {!r}'.format(expr))
return domain
def tosympy(self):
- """
- Return an expression as a sympy object.
- """
import sympy
constraints = []
for equality in self.equalities:
class EmptyType(Polyhedron):
+ """
+ The empty polyhedron, whose set of constraints is not satisfiable.
+ """
__slots__ = Polyhedron.__slots__
class UniverseType(Polyhedron):
+ """
+ The universe polyhedron, whose set of constraints is always satisfiable,
+ i.e. is empty.
+ """
__slots__ = Polyhedron.__slots__
def _polymorphic(func):
@functools.wraps(func)
def wrapper(left, right):
- if not isinstance(left, Expression):
+ if not isinstance(left, LinExpr):
if isinstance(left, numbers.Rational):
left = Rational(left)
else:
raise TypeError('left must be a a rational number '
'or a linear expression')
- if not isinstance(right, Expression):
+ if not isinstance(right, LinExpr):
if isinstance(right, numbers.Rational):
right = Rational(right)
else:
@_polymorphic
def Lt(left, right):
"""
- Assert first set is less than the second set.
+ Create the polyhedron with constraints expr1 < expr2 < expr3 ...
"""
return Polyhedron([], [right - left - 1])
@_polymorphic
def Le(left, right):
"""
- Assert first set is less than or equal to the second set.
+ Create the polyhedron with constraints expr1 <= expr2 <= expr3 ...
"""
return Polyhedron([], [right - left])
@_polymorphic
def Eq(left, right):
"""
- Assert first set is equal to the second set.
+ Create the polyhedron with constraints expr1 == expr2 == expr3 ...
"""
return Polyhedron([left - right], [])
@_polymorphic
def Ne(left, right):
"""
- Assert first set is not equal to the second set.
+ Create the domain such that expr1 != expr2 != expr3 ... The result is a
+ Domain, not a Polyhedron.
"""
return ~Eq(left, right)
@_polymorphic
def Gt(left, right):
"""
- Assert first set is greater than the second set.
+ Create the polyhedron with constraints expr1 > expr2 > expr3 ...
"""
return Polyhedron([], [left - right - 1])
@_polymorphic
def Ge(left, right):
"""
- Assert first set is greater than or equal to the second set.
+ Create the polyhedron with constraints expr1 >= expr2 >= expr3 ...
"""
return Polyhedron([], [left - right])
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