Tr

Tr[m] gives the trace of a square matrix (sum of diagonal elements).

Examples

Compute matrix trace:

Tr[{{1, 2}, {3, 4}}]
(* 5 *)

Tr[IdentityMatrix[3]]
(* 3 *)

(* Trace with symbolic elements *)
Tr[{{a, b}, {c, d}}]
(* a + d *)

Please visit the official Wolfram Language Reference for more details.