/**
     * init graph
     */
    public MetadataGraph(int nVertices) {
        init(nVertices, 2 * nVertices);
    }

    public MetadataGraph(int nVertices, int nEdges) {
        init(nVertices, nEdges);
    }
    // ------------------------------------------------------------------------
    /**
     * construct a single vertex
     */
    public MetadataGraph(MetadataGraphVertex entry) throws MetadataResolutionException {