  The core vertex set of a graph is an invariant of the graph. It consists of
those vertices associated with the non-zero entries of the nullspace vectors of
a $\{0,1\}$-adjacency matrix. The remaining vertices of the graph form the
core--forbidden vertex set. For graphs with independent core vertices, such as
bipartite minimal configurations and trees, the nullspace induces a well
defined three part vertex partition. The parts of this partition are the core
vertex set, their neighbours and the remote core--forbidden vertices. The set
of the remote core--forbidden vertices are those not adjacent to any core
vertex. We show that this set can be removed, leaving the nullity unchanged. We
show that for graphs with independent core vertices, the submatrix of the
adjacency matrix defining the edges incident to the core vertices determines
the nullity of adjacency matrix. To maximize the number of edges for optimal
network graphs with a specified nullity, we determine which perturbations make
up sufficient conditions for the core vertex set of the adjacency matrix of a
graph to be preserved on adding edges.
