Suppose A=(aij)n×nA=(a_{ij})_{n\times n}A=(aij)n×n is an square matrix. Trace of AAA is the sum of the diagonal entries. trace(A)=Tr(A)=∑i=1naii\text{trace}(A)=\text{Tr}(A)=\sum_{i=1}^n{a_{ii}} trace(A)=Tr(A)=i=1∑naii Trace is also equal to the sum of eigenvalues. trace(A)=∑λi where λi∈spectrum of A\text{trace}(A)=\sum{\lambda_i}\text{ where } \lambda_i \in \text{spectrum of } A trace(A)=∑λi where λi∈spectrum of A