Examples of parents endowed with multiple realizations

class sage.categories.examples.with_realizations.SubsetAlgebra(R, S)

Bases: UniqueRepresentation, Parent

An example of parent endowed with several realizations

We consider an algebra \(A(S)\) whose bases are indexed by the subsets \(s\) of a given set \(S\). We consider three natural basis of this algebra: F, In, and Out. In the first basis, the product is given by the union of the indexing sets. That is, for any \(s, t\subset S\)

\[F_s F_t = F_{s\cup t}\]

The In basis and Out basis are defined respectively by:

\[In_s = \sum_{t\subset s} F_t \qquad\text{and}\qquad F_s = \sum_{t\supset s} Out_t\]

Each such basis gives a realization of \(A\), where the elements are represented by their expansion in this basis.

This parent, and its code, demonstrate how to implement this algebra and its three realizations, with coercions and mixed arithmetic between them.

See also

• Sets().WithRealizations

• the Implementing Algebraic Structures thematic tutorial.

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: A.base_ring()
Rational Field

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> A.base_ring()
Rational Field

The three bases of A:

Sage

sage: F   = A.F()  ; F
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
sage: In  = A.In() ; In
The subset algebra of {1, 2, 3} over Rational Field in the In basis
sage: Out = A.Out(); Out
The subset algebra of {1, 2, 3} over Rational Field in the Out basis

Python

>>> from sage.all import *
>>> F   = A.F()  ; F
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
>>> In  = A.In() ; In
The subset algebra of {1, 2, 3} over Rational Field in the In basis
>>> Out = A.Out(); Out
The subset algebra of {1, 2, 3} over Rational Field in the Out basis

One can quickly define all the bases using the following shortcut:

Sage

sage: A.inject_shorthands()
Defining F as shorthand for The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
Defining In as shorthand for The subset algebra of {1, 2, 3} over Rational Field in the In basis
Defining Out as shorthand for The subset algebra of {1, 2, 3} over Rational Field in the Out basis

Python

>>> from sage.all import *
>>> A.inject_shorthands()
Defining F as shorthand for The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
Defining In as shorthand for The subset algebra of {1, 2, 3} over Rational Field in the In basis
Defining Out as shorthand for The subset algebra of {1, 2, 3} over Rational Field in the Out basis

Accessing the basis elements is done with basis() method:

Sage

sage: F.basis().list()
[F[{}], F[{1}], F[{2}], F[{3}], F[{1, 2}], F[{1, 3}], F[{2, 3}], F[{1, 2, 3}]]

Python

>>> from sage.all import *
>>> F.basis().list()
[F[{}], F[{1}], F[{2}], F[{3}], F[{1, 2}], F[{1, 3}], F[{2, 3}], F[{1, 2, 3}]]

To access a particular basis element, you can use the from_set() method:

Sage

sage: F.from_set(2,3)
F[{2, 3}]
sage: In.from_set(1,3)
In[{1, 3}]

Python

>>> from sage.all import *
>>> F.from_set(Integer(2),Integer(3))
F[{2, 3}]
>>> In.from_set(Integer(1),Integer(3))
In[{1, 3}]

or as a convenient shorthand, one can use the following notation:

Sage

sage: F[2,3]
F[{2, 3}]
sage: In[1,3]
In[{1, 3}]

Python

>>> from sage.all import *
>>> F[Integer(2),Integer(3)]
F[{2, 3}]
>>> In[Integer(1),Integer(3)]
In[{1, 3}]

Some conversions:

Sage

sage: F(In[2,3])
F[{}] + F[{2}] + F[{3}] + F[{2, 3}]
sage: In(F[2,3])
In[{}] - In[{2}] - In[{3}] + In[{2, 3}]

sage: Out(F[3])
Out[{3}] + Out[{1, 3}] + Out[{2, 3}] + Out[{1, 2, 3}]
sage: F(Out[3])
F[{3}] - F[{1, 3}] - F[{2, 3}] + F[{1, 2, 3}]

sage: Out(In[2,3])
Out[{}] + Out[{1}] + 2*Out[{2}] + 2*Out[{3}] + 2*Out[{1, 2}] + 2*Out[{1, 3}] + 4*Out[{2, 3}] + 4*Out[{1, 2, 3}]

Python

>>> from sage.all import *
>>> F(In[Integer(2),Integer(3)])
F[{}] + F[{2}] + F[{3}] + F[{2, 3}]
>>> In(F[Integer(2),Integer(3)])
In[{}] - In[{2}] - In[{3}] + In[{2, 3}]

>>> Out(F[Integer(3)])
Out[{3}] + Out[{1, 3}] + Out[{2, 3}] + Out[{1, 2, 3}]
>>> F(Out[Integer(3)])
F[{3}] - F[{1, 3}] - F[{2, 3}] + F[{1, 2, 3}]

>>> Out(In[Integer(2),Integer(3)])
Out[{}] + Out[{1}] + 2*Out[{2}] + 2*Out[{3}] + 2*Out[{1, 2}] + 2*Out[{1, 3}] + 4*Out[{2, 3}] + 4*Out[{1, 2, 3}]

We can now mix expressions:

Sage

sage: (1 + Out[1]) * In[2,3]
Out[{}] + 2*Out[{1}] + 2*Out[{2}] + 2*Out[{3}] + 2*Out[{1, 2}] + 2*Out[{1, 3}] + 4*Out[{2, 3}] + 4*Out[{1, 2, 3}]

Python

>>> from sage.all import *
>>> (Integer(1) + Out[Integer(1)]) * In[Integer(2),Integer(3)]
Out[{}] + 2*Out[{1}] + 2*Out[{2}] + 2*Out[{3}] + 2*Out[{1, 2}] + 2*Out[{1, 3}] + 4*Out[{2, 3}] + 4*Out[{1, 2, 3}]

class Bases(parent_with_realization)

Bases: Category_realization_of_parent

The category of the realizations of the subset algebra

class ParentMethods

Bases: object

from_set(*args)

Construct the monomial indexed by the set containing the elements passed as arguments.

EXAMPLES:

Sage

sage: In = Sets().WithRealizations().example().In(); In
The subset algebra of {1, 2, 3} over Rational Field in the In basis
sage: In.from_set(2,3)
In[{2, 3}]

Python

>>> from sage.all import *
>>> In = Sets().WithRealizations().example().In(); In
The subset algebra of {1, 2, 3} over Rational Field in the In basis
>>> In.from_set(Integer(2),Integer(3))
In[{2, 3}]

As a shorthand, one can construct elements using the following notation:

Sage

sage: In[2,3]
In[{2, 3}]

Python

>>> from sage.all import *
>>> In[Integer(2),Integer(3)]
In[{2, 3}]

one()

Returns the unit of this algebra.

This default implementation takes the unit in the fundamental basis, and coerces it in self.

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: In = A.In(); Out = A.Out()
sage: In.one()
In[{}]
sage: Out.one()
Out[{}] + Out[{1}] + Out[{2}] + Out[{3}] + Out[{1, 2}] + Out[{1, 3}] + Out[{2, 3}] + Out[{1, 2, 3}]

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> In = A.In(); Out = A.Out()
>>> In.one()
In[{}]
>>> Out.one()
Out[{}] + Out[{1}] + Out[{2}] + Out[{3}] + Out[{1, 2}] + Out[{1, 3}] + Out[{2, 3}] + Out[{1, 2, 3}]

super_categories()

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: C = A.Bases(); C
Category of bases of The subset algebra of {1, 2, 3} over Rational Field
sage: C.super_categories()
[Category of realizations of The subset algebra of {1, 2, 3} over Rational Field,
 Join of Category of algebras with basis over Rational Field and
         Category of commutative algebras over Rational Field and
         Category of realizations of unital magmas]

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> C = A.Bases(); C
Category of bases of The subset algebra of {1, 2, 3} over Rational Field
>>> C.super_categories()
[Category of realizations of The subset algebra of {1, 2, 3} over Rational Field,
 Join of Category of algebras with basis over Rational Field and
         Category of commutative algebras over Rational Field and
         Category of realizations of unital magmas]

F

alias of Fundamental

class Fundamental(A)

Bases: CombinatorialFreeModule, BindableClass

The Subset algebra, in the fundamental basis

INPUT:

• A – a parent with realization in SubsetAlgebra

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example()
sage: A.F()
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
sage: A.Fundamental()
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example()
>>> A.F()
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
>>> A.Fundamental()
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis

one()

Return the multiplicative unit element.

EXAMPLES:

Sage

sage: A = AlgebrasWithBasis(QQ).example()                           # needs sage.combinat sage.modules
sage: A.one_basis()                                                 # needs sage.combinat sage.modules
word:
sage: A.one()                                                       # needs sage.combinat sage.modules
B[word: ]

Python

>>> from sage.all import *
>>> A = AlgebrasWithBasis(QQ).example()                           # needs sage.combinat sage.modules
>>> A.one_basis()                                                 # needs sage.combinat sage.modules
word:
>>> A.one()                                                       # needs sage.combinat sage.modules
B[word: ]

one_basis()

Returns the index of the basis element which is equal to ‘1’.

EXAMPLES:

Sage

sage: F = Sets().WithRealizations().example().F(); F
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
sage: F.one_basis()
{}
sage: F.one()
F[{}]

Python

>>> from sage.all import *
>>> F = Sets().WithRealizations().example().F(); F
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
>>> F.one_basis()
{}
>>> F.one()
F[{}]

product_on_basis(left, right)

Product of basis elements, as per AlgebrasWithBasis.ParentMethods.product_on_basis().

INPUT:

• left, right – sets indexing basis elements

EXAMPLES:

Sage

sage: F = Sets().WithRealizations().example().F(); F
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
sage: S = F.basis().keys(); S
Subsets of {1, 2, 3}
sage: F.product_on_basis(S([]), S([]))
F[{}]
sage: F.product_on_basis(S({1}), S({3}))
F[{1, 3}]
sage: F.product_on_basis(S({1,2}), S({2,3}))
F[{1, 2, 3}]

Python

>>> from sage.all import *
>>> F = Sets().WithRealizations().example().F(); F
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis
>>> S = F.basis().keys(); S
Subsets of {1, 2, 3}
>>> F.product_on_basis(S([]), S([]))
F[{}]
>>> F.product_on_basis(S({Integer(1)}), S({Integer(3)}))
F[{1, 3}]
>>> F.product_on_basis(S({Integer(1),Integer(2)}), S({Integer(2),Integer(3)}))
F[{1, 2, 3}]

class In(A)

Bases: CombinatorialFreeModule, BindableClass

The Subset Algebra, in the In basis

INPUT:

• A – a parent with realization in SubsetAlgebra

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example()
sage: A.In()
The subset algebra of {1, 2, 3} over Rational Field in the In basis

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example()
>>> A.In()
The subset algebra of {1, 2, 3} over Rational Field in the In basis

class Out(A)

Bases: CombinatorialFreeModule, BindableClass

The Subset Algebra, in the \(Out\) basis

INPUT:

• A – a parent with realization in SubsetAlgebra

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example()
sage: A.Out()
The subset algebra of {1, 2, 3} over Rational Field in the Out basis

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example()
>>> A.Out()
The subset algebra of {1, 2, 3} over Rational Field in the Out basis

a_realization()

Returns the default realization of self

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: A.a_realization()
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> A.a_realization()
The subset algebra of {1, 2, 3} over Rational Field in the Fundamental basis

base_set()

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: A.base_set()
{1, 2, 3}

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> A.base_set()
{1, 2, 3}

indices()

The objects that index the basis elements of this algebra.

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: A.indices()
Subsets of {1, 2, 3}

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> A.indices()
Subsets of {1, 2, 3}

indices_key(x)

A key function on a set which gives a linear extension of the inclusion order.

INPUT:

• x – set

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: sorted(A.indices(), key=A.indices_key)
[{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}]

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> sorted(A.indices(), key=A.indices_key)
[{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}]

supsets(set)

Returns all the subsets of \(S\) containing set

INPUT:

• set – a subset of the base set \(S\) of self

EXAMPLES:

Sage

sage: A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
sage: A.supsets(Set((2,)))
[{1, 2, 3}, {2, 3}, {1, 2}, {2}]

Python

>>> from sage.all import *
>>> A = Sets().WithRealizations().example(); A
The subset algebra of {1, 2, 3} over Rational Field
>>> A.supsets(Set((Integer(2),)))
[{1, 2, 3}, {2, 3}, {1, 2}, {2}]