The irreducible control property in matrix groups

TL;DR

This paper investigates matrix decompositions within subvarieties of matrix groups, establishing conditions under which the solution set is irreducible and providing bounds on the length of sequences of one-parameter subgroups.

Contribution

It introduces conditions ensuring irreducibility of solution sets in matrix decompositions and constructs explicit sequences of one-parameter subgroups with bounded length.

Findings

Solution sets are irreducible under certain conditions.

Every connected matrix group admits a bounded-length sequence of one-parameter subgroups.

The sequence length is less than 1.5 times the group's dimension.

Abstract

This paper concerns matrix decompositions in which the factors are restricted to lie in a closed subvariety of a matrix group. Such decompositions are of relevance in control theory: given a target matrix in the group, can it be decomposed as a product of elements in the subvarieties, in a given order? And if so, what can be said about the solution set to this problem? Can an irreducible curve of target matrices be lifted to an irreducible curve of factorisations? We show that under certain conditions, for a sufficiently long and complicated such sequence, the solution set is always irreducible, and we show that every connected matrix group has a sequence of one-parameter subgroups that satisfies these conditions, where the sequence has length less than 1.5 times the dimension of the group.