@Override
    public PageRankVertexProgram clone() {
        try {
            final PageRankVertexProgram clone = (PageRankVertexProgram) super.clone();
            if (null != this.initialRankTraversal)
                clone.initialRankTraversal = this.initialRankTraversal.clone();
            return clone;
        } catch (final CloneNotSupportedException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/ranking/pagerank/PageRankVertexProgram.java