public FloydWarshallPredecessorRecorderReducer(IVertexPredecessorMatrix predecessors)
        {
            if (predecessors==null)
                throw new ArgumentNullException(@"predecessors");

            this.predecessors=predecessors;
        }
        public FloydWarshallPredecessorRecorderReducer(IVertexPredecessorMatrix predecessors)
        {
            if (predecessors == null)
            {
                throw new ArgumentNullException(@"predecessors");
            }

            this.predecessors = predecessors;
        }