sage-main / sage / combinat / integer_matrices.py

r"""
Counting, generating, and manipulating non-negative integer matrices

Counting, generating, and manipulating non-negative integer matrices with
prescribed row sums and column sums.

AUTHORS:

- Franco Saliola
"""
#*****************************************************************************
#       Copyright (C) 2012 Franco Saliola <saliola@gmail.com>
#
#  Distributed under the terms of the GNU General Public License (GPL)
#                  http://www.gnu.org/licenses/
#*****************************************************************************

from sage.structure.unique_representation import UniqueRepresentation
from sage.structure.parent import Parent
from sage.categories.finite_enumerated_sets import FiniteEnumeratedSets
from sage.combinat.integer_list import IntegerListsLex
from sage.matrix.constructor import matrix
from sage.rings.integer_ring import ZZ

class IntegerMatrices(UniqueRepresentation, Parent):
    r"""
    The class of non-negative integer matrices with
    prescribed row sums and column sums.

    An *integer matrix* `m` with column sums `c := (c_1,...,c_k)` and row
    sums `l := (l_1,...,l_n)` where `c_1+...+c_k` is equal to `l_1+...+l_n`,
    is a `n \times k` matrix `m = (m_{i,j})` such that
    `m_{1,j}+\dots+m_{n,j} = c_j`, for all `j` and
    `m_{i,1}+\dots+m_{i,k} = l_i`, for all `i`.

    EXAMPLES:

    There are `6` integer matrices with row sums `[3,2,2]` and column sums
    `[2,5]`::

        sage: from sage.combinat.integer_matrices import IntegerMatrices
        sage: IM = IntegerMatrices([3,2,2], [2,5]); IM
        Non-negative integer matrices with row sums [3, 2, 2] and column sums [2, 5]
        sage: IM.list()
        [
        [2 1]  [1 2]  [1 2]  [0 3]  [0 3]  [0 3]
        [0 2]  [1 1]  [0 2]  [2 0]  [1 1]  [0 2]
        [0 2], [0 2], [1 1], [0 2], [1 1], [2 0]
        ]
        sage: IM.cardinality()
        6

    """
    @staticmethod
    def __classcall__(cls, row_sums, column_sums):
        r"""
        Normalize the inputs so that they are hashable.

        INPUT:

        - ``row_sums`` -- list, tuple, or anything defining a Composition
        - ``column_sums`` -- list, tuple, or anything defining a Composition

        EXAMPLES::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IM = IntegerMatrices([4,4,5], [3,7,1,2]); IM
            Non-negative integer matrices with row sums [4, 4, 5] and column sums [3, 7, 1, 2]
            sage: IM = IntegerMatrices((4,4,5), (3,7,1,2)); IM
            Non-negative integer matrices with row sums [4, 4, 5] and column sums [3, 7, 1, 2]
            sage: IM = IntegerMatrices(Composition([4,4,5]), Composition([3,7,1,2])); IM
            Non-negative integer matrices with row sums [4, 4, 5] and column sums [3, 7, 1, 2]

        """
        from sage.combinat.composition import Composition
        row_sums = Composition(row_sums)
        column_sums = Composition(column_sums)
        return super(IntegerMatrices, cls).__classcall__(cls, row_sums, column_sums)

    def __init__(self, row_sums, column_sums):
        r"""
        Constructor of this class; for documentation, see
        :class:`IntegerMatrices`.

        INPUT:

        - ``row_sums`` -- Composition
        - ``column_sums`` -- Composition

        TESTS::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IM = IntegerMatrices([3,2,2], [2,5]); IM
            Non-negative integer matrices with row sums [3, 2, 2] and column sums [2, 5]
            sage: TestSuite(IM).run()
        """
        self._row_sums = row_sums
        self._col_sums = column_sums
        Parent.__init__(self, category=FiniteEnumeratedSets())

    def _repr_(self):
        r"""
        TESTS::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IntegerMatrices([3,2,2], [2,5])._repr_()
            'Non-negative integer matrices with row sums [3, 2, 2] and column sums [2, 5]'
        """
        return "Non-negative integer matrices with row sums %s and column sums %s" % \
                        (self._row_sums, self._col_sums)

    def __iter__(self):
        r"""
        An iterator for the integer matrices with the prescribed row sums and
        columns sums.

        EXAMPLES::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IntegerMatrices([2,2], [1,2,1]).list()
            [
            [1 1 0]  [1 0 1]  [0 2 0]  [0 1 1]
            [0 1 1], [0 2 0], [1 0 1], [1 1 0]
            ]
            sage: IntegerMatrices([0,0],[0,0,0]).list()
            [
            [0 0 0]
            [0 0 0]
            ]
            sage: IntegerMatrices([1,1],[1,1]).list()
            [
            [1 0]  [0 1]
            [0 1], [1 0]
            ]

        """
        for x in integer_matrices_generator(self._row_sums, self._col_sums):
            yield matrix(ZZ, x)

    def __contains__(self, x):
        r"""
        Tests if ``x`` is an element of ``self``.

        INPUT:

        - ``x`` -- matrix

        EXAMPLES::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IM = IntegerMatrices([4], [1,2,1])
            sage: matrix([[1, 2, 1]]) in IM
            True
            sage: matrix(QQ, [[1, 2, 1]]) in IM
            True
            sage: matrix([[2, 1, 1]]) in IM
            False

        TESTS::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IM = IntegerMatrices([4], [1,2,1])
            sage: [1, 2, 1] in IM
            False
            sage: matrix([[-1, 3, 1]]) in IM
            False

        """
        from sage.matrix.matrix import Matrix
        if not isinstance(x, Matrix):
            return False
        row_sums = [ZZ.zero()] * x.nrows()
        col_sums = [ZZ.zero()] * x.ncols()
        for i in range(x.nrows()):
            for j in range(x.ncols()):
                x_ij = x[i, j]
                if x_ij not in ZZ or x_ij < 0:
                    return False
                row_sums[i] += x_ij
                col_sums[j] += x_ij
            if row_sums[i] != self._row_sums[i]:
                return False
        if col_sums != self._col_sums:
            return False
        return True

    def cardinality(self):
        r"""
        The number of integer matrices with the prescribed row sums and columns
        sums.

        EXAMPLES::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IntegerMatrices([2,5], [3,2,2]).cardinality()
            6
            sage: IntegerMatrices([1,1,1,1,1], [1,1,1,1,1]).cardinality()
            120
            sage: IntegerMatrices([2,2,2,2], [2,2,2,2]).cardinality()
            282
            sage: IntegerMatrices([4], [3]).cardinality()
            0
            sage: len(IntegerMatrices([0,0], [0]).list())
            1

        This method computes the cardinality using symmetric functions. Below
        are the same examples, but computed by generating the actual matrices::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: len(IntegerMatrices([2,5], [3,2,2]).list())
            6
            sage: len(IntegerMatrices([1,1,1,1,1], [1,1,1,1,1]).list())
            120
            sage: len(IntegerMatrices([2,2,2,2], [2,2,2,2]).list())
            282
            sage: len(IntegerMatrices([4], [3]).list())
            0
            sage: len(IntegerMatrices([0], [0]).list())
            1

        """
        from sage.combinat.sf.sf import SymmetricFunctions
        from sage.combinat.partition import Partition
        h = SymmetricFunctions(ZZ).homogeneous()
        row_partition = Partition(sorted(self._row_sums, reverse=True))
        col_partition = Partition(sorted(self._col_sums, reverse=True))
        return h[row_partition].scalar(h[col_partition])

    def row_sums(self):
        r"""
        The row sums of the integer matrices in ``self``.

        OUTPUT:

        - Composition

        EXAMPLES::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IM = IntegerMatrices([3,2,2], [2,5])
            sage: IM.row_sums()
            [3, 2, 2]
        """
        return self._row_sums

    def column_sums(self):
        r"""
        The column sums of the integer matrices in ``self``.

        OUTPUT:

        - Composition

        EXAMPLES::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IM = IntegerMatrices([3,2,2], [2,5])
            sage: IM.column_sums()
            [2, 5]
        """
        return self._col_sums

    def to_composition(self, x):
        r"""
        The composition corresponding to the integer matrix.

        This is the composition obtained by reading the entries of the matrix
        from left to right along each row, and reading the rows from top to
        bottom, ignore zeros.

        INPUT:

        - ``x`` -- matrix

        EXAMPLES::

            sage: from sage.combinat.integer_matrices import IntegerMatrices
            sage: IM = IntegerMatrices([3,2,2], [2,5]); IM
            Non-negative integer matrices with row sums [3, 2, 2] and column sums [2, 5]
            sage: IM.list()
            [
            [2 1]  [1 2]  [1 2]  [0 3]  [0 3]  [0 3]
            [0 2]  [1 1]  [0 2]  [2 0]  [1 1]  [0 2]
            [0 2], [0 2], [1 1], [0 2], [1 1], [2 0]
            ]
            sage: for m in IM: print IM.to_composition(m)
            [2, 1, 2, 2]
            [1, 2, 1, 1, 2]
            [1, 2, 2, 1, 1]
            [3, 2, 2]
            [3, 1, 1, 1, 1]
            [3, 2, 2]
        """
        from sage.combinat.composition import Composition
        return Composition([entry for row in x for entry in row if entry != 0])

def integer_matrices_generator(row_sums, column_sums):
    r"""
    Recursively generate the integer matrices with the prescribed row sums and
    column sums.

    INPUT:

    - ``row_sums`` -- list or tuple
    - ``column_sums`` -- list or tuple

    OUTPUT:

    - an iterator producing a list of lists

    EXAMPLES::

        sage: from sage.combinat.integer_matrices import integer_matrices_generator
        sage: iter = integer_matrices_generator([3,2,2], [2,5]); iter
        <generator object integer_matrices_generator at ...>
        sage: for m in iter: print m
        [[2, 1], [0, 2], [0, 2]]
        [[1, 2], [1, 1], [0, 2]]
        [[1, 2], [0, 2], [1, 1]]
        [[0, 3], [2, 0], [0, 2]]
        [[0, 3], [1, 1], [1, 1]]
        [[0, 3], [0, 2], [2, 0]]

    """
    row_sums = list(row_sums)
    column_sums = list(column_sums)
    if sum(row_sums) != sum(column_sums):
        raise StopIteration
    if len(row_sums) == 0:
        yield []
    elif len(row_sums) == 1:
        yield [column_sums]
    else:
        for comp in IntegerListsLex(row_sums[0], len(column_sums), ceiling=column_sums):
            t = [column_sums[i]-ci for (i, ci) in enumerate(comp)]
            for mat in integer_matrices_generator(row_sums[1:], t):
                yield [list(comp)] + mat
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