https://cis.temple.edu/~latecki/Courses/CIS2166-Fall16/Lectures/MatrixAlg1.pdf
A matrix is a rectangular array of numbers or other mathematical objects, for which operations such as addition and multiplication are defined. Most of this article focuses on real matrices, i.e., matrices whose elements are real numbers. For instance, this is a real matrix: The numbers, symbols or expressions in the matrix are called its entries or its elements. The horizontal and vertical ...