  In this report, we describe a novel graph invariant for computational graphs
(colored directed acylic graphs) and how we used it to generate all distinct
computational graphs up to isomorphism for small graphs. The algorithm
iteratively applies isomorphism-invariant operations, which take into account
the graph structure and coloring, and outputs a fixed-length hash that is
identical for all isomorphic computational graphs. While the algorithm cannot
perfectly distinguish all pairs of non-isomorphic computational graphs, we
suggest that it may be useful as a heuristic for comparing graphs.
