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A square or rectangular set of numbers, usually written enclosed in a large pair of brackets. There are special rules for adding and multiplying matrices that make them handy in representing linear transformations.
For example, the equations

x + 2y + 3z = 1 2x + 5y + 7z = 2 x + 4y = 3

can be represented by the single matrix equation

Ax = B

where

A =      1 2 3 2 5 7 1 4 0      ,    x =      x y z      ,   and  B =      1 2 3      .

Matrices can represent many physical quantities which have multiple components in a simple but useful form. For example, the various moments of inertia that a solid has about different axes of rotation can be expressed in a single 3 ×3 matrix.