  This paper addresses a structural design problem in control systems, and
explicitly takes into consideration the possible application to large-scale
systems. More precisely, we aim to determine and characterize the minimum
number of manipulated state variables ensuring structural controllability of
switched linear continuous-time systems. Towards this goal, we provide a new
necessary and sufficient condition that leverages both graph-theoretic and
algebraic properties required to ensure feasibility of the solutions. With this
new condition, we show that a solution can be determined by an efficient
procedure, i.e., polynomial in the number of state variables. In addition, we
also discuss the switching signal properties that ensure structural
controllability and the computational complexity of determining these
sequences. In particular, we show that determining the minimum number of modes
that a switching signal requires to ensure structural controllability is
NP-hard.
