1 line
133 B
Plaintext
1 line
133 B
Plaintext
$$\tr (AB) = \sum_{i=1}^n (AB)_{ii} = \sum_{i=1}^n \sum_{k=1}^n a_{ik} b_{ki} = \sum_{k=1}^n \sum_{i=1}^n b_{ki} a_{ik} = \tr (BA).$$ |