What is the Laplacian matrix of a graph?

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What is the Laplacian matrix of a graph?

The Laplacian matrix of a graph is a square matrix that represents the structure of the graph. It is defined as the difference between the degree matrix and the adjacency matrix of the graph.

To construct the Laplacian matrix, we first need to calculate the degree matrix. The degree matrix is a diagonal matrix where each diagonal entry represents the degree of the corresponding vertex in the graph.

Next, we calculate the adjacency matrix, which is a matrix that represents the connections between vertices in the graph. The adjacency matrix has a value of 1 if there is an edge between two vertices, and 0 otherwise.

Finally, we subtract the adjacency matrix from the degree matrix to obtain the Laplacian matrix. The Laplacian matrix is symmetric, with the diagonal entries representing the degree of each vertex, and the off-diagonal entries representing the negative of the number of edges between the corresponding vertices.

The Laplacian matrix is a fundamental tool in graph theory as it provides important information about the graph's connectivity, eigenvalues, and other properties. It is widely used in various applications, such as spectral graph theory, network analysis, and graph clustering.