Single-entry matrix

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–In mathematics a single-entry matrix is a matrix where a single element is one and the rest of the elements are zero,[1][2] 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.:

Alternatively, a column-selector when multiplied on the right side:

The name, single-entry matrix, is not common, but seen in a few works.[3]


  1. ^ Kaare Brandt Petersen & Michael Syskind Pedersen (2008-02-16). "The Matrix Cookbook" (PDF). 
  2. ^ Shohei Shimizu, Patrick O. Hoyer, Aapo Hyvärinen & Antti Kerminen (2006). "A Linear Non-Gaussian Acyclic Model for Causal Discovery" (PDF). Journal of Machine Learning Research. 7: 2003–2030. 
  3. ^ Examples: