# Econometric Theory/Definitions

## Identity Matrix

editThe identity matrix, with a size of *n*, is an *n*-by-*n* square matrix with ones on the main diagonal and zeros elsewhere. It is commonly denoted as , or simply by *I* if the size is immaterial or can be easily determined by the context.

The most important property of the identity matrix is that, when multiplied by another matrix, *A*, the result will be *A*

- and .