Spark in Action

Appendix C. A primer on linear algebra

This appendix presents the basic linear algebra operations. They’re important for understanding much of the math behind most machine-learning algorithms. In case you skipped your linear algebra classes, this is your chance to come to grips with it.

Matrices and vectors

A matrix is a set of elements arranged in rows and columns (we’ll only use matrices whose elements are numbers). This is a matrix with two rows and three columns, so it’s called a 2 × 3 matrix:

Usually, the number of rows in a matrix is denoted by the letter m and the number of columns by the letter n. m and n are the matrix’s dimensions, ...