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