Definition:Unit Matrix

Also known as
Some sources call this the unit matrix and denote it $\mathbf 1$ or $\mathbf 1_n$.

In physics and mechanics it is common to see $\mathbf I$ used specifically to denote the $3 \times 3$ identity matrix.

Also see

 * Identity Matrix is Unity of Ring of Square Matrices, which demonstrates the equivalence of these definitions.


 * Compare with, but do not confuse with, the Definition:Ones Matrix.