Single-entry matrix

In mathematics a single-entry matrix is a matrix where a single element is one and the rest of the elements are zero, e.g., In mathematics a single-entry matrix is a matrix where a single element is one and the rest of the elements are zero, e.g., It is a specific type of a sparse matrix. The single-entry matrix can be regarded a row-selector when it is multiplied on the left side of the matrix, e.g.: