Hardly worth coding, if it didn't appear in so many formulae in psychometrics, the trace of a (square) matrix is just the sum of the diagonal elements.
Usage
tr(m)
Arguments
m
A square matrix
Value
The sum of the diagonal elements of a square matrix.
i.e. tr(m) <- sum(diag(m)).
Details
The tr function is used in various matrix operations and is the sum of the diagonal elements of a matrix.