XGitUrl: https://scm.cri.ensmp.fr/git/linpy.git/blobdiff_plain/c9bd08381cbc109ae9602cc780fc7e8899651ae3..ba15f3f33f837b1291f74bc94081e99b860d3228:/linpy/polyhedra.py?ds=sidebyside
diff git a/linpy/polyhedra.py b/linpy/polyhedra.py
index 346ffff..b486be1 100644
 a/linpy/polyhedra.py
+++ b/linpy/polyhedra.py
@@ 36,8 +36,11 @@ __all__ = [
class Polyhedron(Domain):
"""
 Polyhedron class allows users to build and inspect polyherons. Polyhedron inherits from 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',
'_inequalities',
@@ 48,9 +51,35 @@ class Polyhedron(Domain):
def __new__(cls, equalities=None, inequalities=None):
"""
 Create and return a new Polyhedron from a string or list of equalities and inequalities.
 """
+ 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')
@@ 80,21 +109,24 @@ class Polyhedron(Domain):
@property
def equalities(self):
"""
 Return a list of the equalities in a polyhedron.
+ 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 polyhedron.
+ 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 the list of the constraints of a polyhedron.
+ The tuple of constraints, i.e., equalities and inequalities. This is
+ semantically equivalent to: equalities + inequalities.
"""
return self._constraints
@@ 103,15 +135,9 @@ class Polyhedron(Domain):
return self,
def make_disjoint(self):
 """
 Return a polyhedron as disjoint.
 """
return self
def isuniverse(self):
 """
 Return true if a polyhedron is the Universe set.
 """
islbset = self._toislbasicset(self.equalities, self.inequalities,
self.symbols)
universe = bool(libisl.isl_basic_set_is_universe(islbset))
@@ 119,15 +145,9 @@ class Polyhedron(Domain):
return universe
def aspolyhedron(self):
 """
 Return the polyhedral hull of a polyhedron.
 """
return self
def __contains__(self, point):
 """
 Report whether a polyhedron constains an integer point
 """
if not isinstance(point, Point):
raise TypeError('point must be a Point instance')
if self.symbols != point.symbols:
@@ 141,10 +161,6 @@ class Polyhedron(Domain):
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)
@@ 158,6 +174,9 @@ class Polyhedron(Domain):
return inequalities
def widen(self, other):
+ """
+ Compute the standard widening of two polyhedra, Ã la Halbwachs.
+ """
if not isinstance(other, Polyhedron):
raise ValueError('argument must be a Polyhedron instance')
inequalities1 = self._asinequalities()
@@ 242,9 +261,6 @@ class Polyhedron(Domain):
@classmethod
def fromstring(cls, string):
 """
 Create and return a Polyhedron from a string.
 """
domain = Domain.fromstring(string)
if not isinstance(domain, Polyhedron):
raise ValueError('nonpolyhedral expression: {!r}'.format(string))
@@ 261,7 +277,6 @@ class Polyhedron(Domain):
else:
return 'And({})'.format(', '.join(strings))

def _repr_latex_(self):
strings = []
for equality in self.equalities:
@@ 272,18 +287,12 @@ class Polyhedron(Domain):
@classmethod
def fromsympy(cls, expr):
 """
 Convert a sympy object to a polyhedron.
 """
domain = Domain.fromsympy(expr)
if not isinstance(domain, Polyhedron):
raise ValueError('nonpolyhedral expression: {!r}'.format(expr))
return domain
def tosympy(self):
 """
 Return a polyhedron as a sympy object.
 """
import sympy
constraints = []
for equality in self.equalities:
@@ 294,6 +303,9 @@ class Polyhedron(Domain):
class EmptyType(Polyhedron):
+ """
+ The empty polyhedron, whose set of constraints is not satisfiable.
+ """
__slots__ = Polyhedron.__slots__
@@ 321,6 +333,10 @@ Empty = EmptyType()
class UniverseType(Polyhedron):
+ """
+ The universe polyhedron, whose set of constraints is always satisfiable,
+ i.e. is empty.
+ """
__slots__ = Polyhedron.__slots__
@@ 363,41 +379,42 @@ def _polymorphic(func):
@_polymorphic
def Lt(left, right):
"""
 Returns a Polyhedron instance with a single constraint as left less than right.
+ Create the polyhedron with constraints expr1 < expr2 < expr3 ...
"""
return Polyhedron([], [right  left  1])
@_polymorphic
def Le(left, right):
"""
 Returns a Polyhedron instance with a single constraint as left less than or equal to right.
+ Create the polyhedron with constraints expr1 <= expr2 <= expr3 ...
"""
return Polyhedron([], [right  left])
@_polymorphic
def Eq(left, right):
"""
 Returns a Polyhedron instance with a single constraint as left equal to right.
+ Create the polyhedron with constraints expr1 == expr2 == expr3 ...
"""
return Polyhedron([left  right], [])
@_polymorphic
def Ne(left, right):
"""
 Returns a Polyhedron instance with a single constraint as left not equal to right.
+ 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):
"""
 Returns a Polyhedron instance with a single constraint as left greater than right.
+ Create the polyhedron with constraints expr1 > expr2 > expr3 ...
"""
return Polyhedron([], [left  right  1])
@_polymorphic
def Ge(left, right):
"""
 Returns a Polyhedron instance with a single constraint as left greater than or equal to right.
+ Create the polyhedron with constraints expr1 >= expr2 >= expr3 ...
"""
return Polyhedron([], [left  right])