The trace of matrix (2 dimensional array) is implemented with tr=: +/@:((<0 1)&|:)
(BTW: The "(<0 1)&|:" always mystifies me.) Can someone point me to an efficient and terse verb that generalises the trace to arbitrary dimensions? A verb that works on 1 and higher than 2 dimensional arrays. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
