For example, if ``x`` is a :class:`Symbol`, then ``x + 1`` is an instance of :class:`LinExpr`.
.. class:: LinExpr(coefficients=None, constant=0)
- LinExpr(string)
+ LinExpr(string)
Return a linear expression from a dictionary or a sequence, that maps 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 one of the following instructions:
+ For example, the linear expression ``x + 2*y + 1`` can be constructed using one of the following instructions:
>>> x, y = symbols('x y')
>>> LinExpr({x: 1, y: 2}, 1)
Alternatively, linear expressions can be constructed from a string:
- >>> LinExpr('x + 2*y + 1')
+ >>> LinExpr('x + 2y + 1')
:class:`LinExpr` instances are hashable, and should be treated as immutable.
>>> x, y = symbols('x y')
>>> x < y
- Le(x - y + 1, 0)
+ x + 1 <= y
.. method:: scaleint()
They are implemented by the :class:`Rational` class, that inherits from both :class:`LinExpr` and :class:`fractions.Fraction` classes.
.. class:: Rational(numerator, denominator=1)
- Rational(string)
+ Rational(string)
The first version requires that the *numerator* and *denominator* are instances of :class:`numbers.Rational` and returns a new :class:`Rational` instance with the value ``numerator/denominator``.
If the denominator is ``0``, it raises a :exc:`ZeroDivisionError`.
This space can be unbounded.
.. class:: Polyhedron(equalities, inequalities)
- Polyhedron(string)
- Polyhedron(geometric object)
+ Polyhedron(string)
+ Polyhedron(geometric object)
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])
+ >>> square
+ And(0 <= x, x <= 2, 0 <= y, y <= 2)
It may be easier to use comparison operators :meth:`LinExpr.__lt__`, :meth:`LinExpr.__le__`, :meth:`LinExpr.__ge__`, :meth:`LinExpr.__gt__`, or functions :func:`Lt`, :func:`Le`, :func:`Eq`, :func:`Ge` and :func:`Gt`, using one of the following instructions:
>>> square = Polyhedron('0 <= x <= 2, 0 <= y <= 2')
>>> square2 = Polyhedron('2 <= x <= 4, 2 <= y <= 4')
>>> Polyhedron(square | square2)
+ And(x <= 4, 0 <= x, y <= 4, 0 <= y, x <= y + 2, y <= x + 2)
A polyhedron is a :class:`Domain` instance, and, therefore, inherits the functionalities of this class.
It is also a :class:`GeometricObject` instance.
Unlike polyhedra, domains allow exact computation of union, subtraction and complementary operations.
.. class:: Domain(*polyhedra)
- Domain(string)
- Domain(geometric object)
+ Domain(string)
+ Domain(geometric object)
Return a domain from a sequence of polyhedra.
>>> square = Polyhedron('0 <= x <= 2, 0 <= y <= 2')
>>> square2 = Polyhedron('2 <= x <= 4, 2 <= y <= 4')
- >>> dom = Domain([square, square2])
+ >>> dom = Domain(square, square2)
+ >>> dom
+ Or(And(x <= 2, 0 <= x, y <= 2, 0 <= y), And(x <= 4, 2 <= x, y <= 4, 2 <= y))
It is also possible to build domains from polyhedra using arithmetic operators :meth:`Domain.__and__`, :meth:`Domain.__or__` or functions :func:`And` and :func:`Or`, using one of the following instructions:
>>> square1 = Le(0, x, 2) & Le(0, y, 2)
>>> square1
-And(Ge(x, 0), Ge(-x + 2, 0), Ge(y, 0), Ge(-y + 2, 0))
+And(0 <= x, x <= 2, 0 <= y, y <= 2)
LinPy provides comparison functions :func:`Lt`, :func:`Le`, :func:`Eq`, :func:`Ne`, :func:`Ge` and :func:`Gt` to build constraints, and logical operators :func:`And`, :func:`Or`, :func:`Not` to combine them.
Alternatively, a polyhedron can be built from a string:
>>> square2 = Polyhedron('1 <= x <= 3, 1 <= y <= 3')
>>> square2
-And(Ge(x - 1, 0), Ge(-x + 3, 0), Ge(y - 1, 0), Ge(-y + 3, 0))
+And(1 <= x, x <= 3, 1 <= y, y <= 3)
The usual polyhedral operations are available, including intersection:
->>> inter = square1.intersection(square2)
+>>> inter = square1.intersection(square2) # or square1 & square2
>>> inter
-And(Ge(x - 1, 0), Ge(-x + 2, 0), Ge(y - 1, 0), Ge(-y + 2, 0))
+And(1 <= x, x <= 2, 1 <= y, y <= 2)
convex union:
>>> hull = square1.convex_union(square2)
>>> hull
-And(Ge(x, 0), Ge(y, 0), Ge(-x + y + 2, 0), Ge(x - y + 2, 0), Ge(-x + 3, 0), Ge(-y + 3, 0))
+And(0 <= x, 0 <= y, x <= y + 2, y <= x + 2, x <= 3, y <= 3)
and projection:
->>> square1.project([y])
-And(Ge(x, 0), Ge(-x + 2, 0))
+>>> proj = square1.project([y])
+>>> proj
+And(0 <= x, x <= 2)
Equality and inclusion tests are also provided.
Special values :data:`Empty` and :data:`Universe` represent the empty and universe polyhedra.
An example of domain is the set union (as opposed to convex union) of polyhedra ``square1`` and ``square2``.
The result is a :class:`Domain` object.
->>> union = square1 | square2
+>>> union = square1.union(square2) # or square1 | square2
>>> union
-Or(And(Ge(-x + 2, 0), Ge(x, 0), Ge(-y + 2, 0), Ge(y, 0)), And(Ge(-x + 3, 0), Ge(x - 1, 0), Ge(-y + 3, 0), Ge(y - 1, 0)))
+Or(And(x <= 2, 0 <= x, y <= 2, 0 <= y), And(x <= 3, 1 <= x, y <= 3, 1 <= y))
>>> union <= hull
True
Unlike polyhedra, domains allow exact computation of union, subtraction and complementary operations.
->>> diff = square1 - square2
+>>> diff = square1.difference(square2) # or square1 - square2
>>> diff
-Or(And(Eq(x, 0), Ge(y, 0), Ge(-y + 2, 0)), And(Eq(y, 0), Ge(x - 1, 0), Ge(-x + 2, 0)))
+Or(And(x == 0, 0 <= y, y <= 2), And(y == 0, 1 <= x, x <= 2))
>>> ~square1
-Or(Ge(-x - 1, 0), Ge(x - 3, 0), And(Ge(x, 0), Ge(-x + 2, 0), Ge(-y - 1, 0)), And(Ge(x, 0), Ge(-x + 2, 0), Ge(y - 3, 0)))
+Or(x + 1 <= 0, 3 <= x, And(0 <= x, x <= 2, y + 1 <= 0), And(0 <= x, x <= 2, 3 <= y))
.. _tutorial_plot: