Tr[list] finds the trace of the matrix or tensor list.
Tr[list, f] finds a generalized trace, combining terms with f instead of Plus.
Tr[list, f, n] goes down to level n in list.
Tr[list] sums the diagonal elements list[[i, i, ... ]].
Tr works for rectangular as well as square matrices and tensors.
Tr can be used on SparseArray objects.
See Section 3.7.7.
See also: Total, Transpose, Det, DiagonalMatrix, Eigenvalues.
New in Version 4.