code: @Override
      public double similarity(int vertexIdx1, int vertexIdx2) {
          if (vertexIdx1 == vertexIdx2)
              return 1.0;
  
          INDArray vector = Transforms.unitVec(getVertexVector(vertexIdx1));
          INDArray vector2 = Transforms.unitVec(getVertexVector(vertexIdx2));
          return Nd4j.getBlasWrapper().dot(vector, vector2);
      }
docs: Returns the cosine similarity of the vector representations of two vertices in the graph,
  given the indices of these verticies
  @return Cosine similarity of two vertices