  Strong structural controllability (SSC) guarantees networked system with
linear-invariant dynamics controllable for all numerical realizations of
parameters. Current research has established algebraic and graph-theoretic
conditions of SSC for zero/nonzero or zero/nonzero/arbitrary structure. One
relevant practical problem is how to fully control the system with the minimal
number of input signals and identify which nodes must be imposed signals.
Previous work shows that this optimization problem is NP-hard and it is
difficult to find the solution. To solve this problem, we formulate the graph
coloring process as a Markov decision process (MDP) according to the
graph-theoretical condition of SSC for both zero/nonzero and
zero/nonzero/arbitrary structure. We use Actor-critic method with Directed
graph neural network which represents the color information of graph to
optimize MDP. Our method is validated in a social influence network with real
data and different complex network models. We find that the number of input
nodes is determined by the average degree of the network and the input nodes
tend to select nodes with low in-degree and avoid high-degree nodes.
