# Vector Partitions¶

AUTHORS:

• Amritanshu Prasad (2013): Initial version
sage.combinat.vector_partition.IntegerVectorsIterator(vect, min=None)

Return an iterator over the list of integer vectors which are componentwise less than or equal to vect, and lexicographically greater than or equal to min.

INPUT:

• vect – A list of non-negative integers
• min – A list of non-negative integers dominated elementwise by vect

OUTPUT:

A list in lexicographic order of all integer vectors (as lists) which are dominated elementwise by vect and are greater than or equal to min in lexicographic order.

EXAMPLES:

sage: from sage.combinat.vector_partition import IntegerVectorsIterator
sage: list(IntegerVectorsIterator([1, 1]))
[[0, 0], [0, 1], [1, 0], [1, 1]]

sage: list(IntegerVectorsIterator([1, 1], min = [1, 0]))
[[1, 0], [1, 1]]

class sage.combinat.vector_partition.VectorPartition(parent, vecpar)

A vector partition is a multiset of integer vectors.

partition_at_vertex(i)

Return the partition obtained by sorting the i-th elements of the vectors in the vector partition.

EXAMPLES:

sage: V = VectorPartition([[1, 2, 1], [2, 4, 1]])
sage: V.partition_at_vertex(1)
[4, 2]

sum()

Return the sum vector as a list.

EXAMPLES:

sage: V = VectorPartition([[3, 2, 1], [2, 2, 1]])
sage: V.sum()
[5, 4, 2]

class sage.combinat.vector_partition.VectorPartitions(vec, min)

Class of all vector partitions of vec with all parts greater than or equal to min in lexicographic order.

A vector partition of vec is a list of vectors with non-negative integer entries whose sum is vec.

INPUT:

• vec – a list of non-negative integers.

EXAMPLES:

If min is not specified, then the class of all vector partitions of vec is created:

sage: VP = VectorPartitions([2, 2])
sage: for vecpar in VP:
....:     print(vecpar)
[[0, 1], [0, 1], [1, 0], [1, 0]]
[[0, 1], [0, 1], [2, 0]]
[[0, 1], [1, 0], [1, 1]]
[[0, 1], [2, 1]]
[[0, 2], [1, 0], [1, 0]]
[[0, 2], [2, 0]]
[[1, 0], [1, 2]]
[[1, 1], [1, 1]]
[[2, 2]]


If min is specified, then the class consists of only those vector partitions whose parts are all greater than or equal to min in lexicographic order:

sage: VP = VectorPartitions([2, 2], min = [1, 0])
sage: for vecpar in VP:
....:     print(vecpar)
[[1, 0], [1, 2]]
[[1, 1], [1, 1]]
[[2, 2]]

Element

alias of VectorPartition

sage.combinat.vector_partition.find_min(vect)

Return a string of 0’s with one 1 at the location where the list vect has its last entry which is not equal to 0.

INPUT:

• vec – A list of integers

OUTPUT:

A list of the same length with 0’s everywhere, except for a 1 at the last position where vec has an entry not equal to 0.

EXAMPLES:

sage: from sage.combinat.vector_partition import find_min
sage: find_min([2, 1])
[0, 1]
sage: find_min([2, 1, 0])
[0, 1, 0]