Nabble-fora are in a sickly state, refusing full perusal, so excuse me if this's been answered.. I wanted an x-dimensional y-rank identity matrix.
With an auxilliary verb to get a main diagonal from an arbitrarily-dimensional square array verb: md=: (|:~(<@i.@#@$)) I assured the following verb yields 1s in the main diagonal and 0s elsewhere: id=: 4 : 0 q=.x(|:@(([,])$i.@]))y x (1 q}([$])$0:) y ) I still do not understand why the below one-liner doesn't suffice, given all individual parts work as intended. Substituting the 1 for, say, a 2 or 9, results in that many filled elements in the first face with that same number (1 1, 2 2s, 9 9s, etc.). (1 (|:@((],[)$i.@[)) }([$])$0:) Anyways, I was immediate struck down, discovering that (+/ .*) doesn't exactly work for >2-dimensional arrays, because of the recursive minor-based action of the dot product, making increasingly ranked array spit out more and more dimensioned results. Worse still, discussing matrix multiplication with two colleagues, I more or less got 'oddly-dimensioned tensor products are iffy'. I was told to first define the multiplication, which would then yield the identity matrix, as opposed to what I did- extending the 2D cased. I'll be looking through some multilinear algebra in my spare time, but I was wondering if there's an accepted way in J )or the other APL family language) for multidimensional multiplication, or if it's best decided on a case by case basis. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
