Definition:Trace (Linear Algebra)/Matrix

Definition
Let $A = \left({a_{ij}}\right)_{1 \mathop \le i, j \mathop \le n}$ be a matrix.

The trace of $A$ is:


 * $\displaystyle \operatorname{tr} \left({A}\right) = \sum_{i \mathop = 1}^n a_{ii}$

Also defined as
Some sources define the trace of a matrix for a square matrix only.