Hollow matrix

In mathematics, a hollow matrix may refer to one of several related classes of matrix. In mathematics, a hollow matrix may refer to one of several related classes of matrix. A hollow matrix may be one with 'few' non-zero entries: that is, a sparse matrix. A hollow matrix may be a square matrix whose diagonal elements are all equal to zero. The most obvious example is the real skew-symmetric matrix. Other examples are the adjacency matrix of a finite simple graph; a distance matrix or Euclidean distance matrix. If A is an n×n hollow matrix, then the elements of A are given by