getSubgraphAdjacencyMatrix(vertexIds) {
    let length = vertexIds.length;
    let adjacencyMatrix = Array(length);

    for (var i = 0; i < length; i++) {
      adjacencyMatrix[i] = new Array(length);
      adjacencyMatrix[i].fill(0);

      for (var j = 0; j < length; j++) {
        if (i === j) {
          continue;
        }

        if (this.hasEdge(vertexIds[i], vertexIds[j])) {
          adjacencyMatrix[i][j] = 1;
        }
      }
    }

    return adjacencyMatrix;
  }
Get the adjacency matrix of a subgraph.

@param {Number[]} vertexIds An array containing the vertex ids contained within the subgraph.
@returns {Array[]} The adjancency matrix of the subgraph.