  In this paper, we study the target controllability problem of networked
dynamical systems, in which we are tasked to steer a subset of network states
towards a desired objective. More specifically, we derive necessary and
sufficient conditions for the structural target controllability problem of
linear time-invariant (LTI) systems with symmetric state matrices, such as
undirected dynamical networks with unknown link weights. To achieve our goal,
we first characterize the generic rank of symmetrically structured matrices, as
well as the modes of any numerical realization. Subsequently, we provide a
graph-theoretic necessary and sufficient condition for the structural
controllability of undirected networks with multiple control nodes. Finally, we
derive a graph-theoretic necessary and sufficient condition for structural
target controllability of undirected networks. Remarkably, apart from the
standard reachability condition, only local topological information is needed
for the verification of structural target controllability.
