Re: [Gretl-devel] matrix multiplication question

On Mon, 26 Sep 2011, Boris Demeshev wrote: I believe that the crux of the matter, as Allin pointed out, is: assume that the sum between a matrix and a scalar is defined in the obvious way. Then, is it possible to find cases when the operaton is _not_ commutative? After some thinking about it, I believe it isn't possible (but then again, neutrinos may be faster than light [http://operaweb.lngs.infn.it/], so you should never say never). As a consequence, IMO (a \pm b) should be ok for any matrix/scalar combination. Actually, I believe that most matrix-oriented languages work more or less like this: use "§" to indicate an arbitrary binary operator which can operate elementwise on matrices. Then A § B is well defined as long as [ rows(A) == rows(B) || rows(A) == 1 || rows(B) == 1 ] && [ cols(A) == cols(B) || cols(A) == 1 || cols(B) == 1 ] which makes it legal, for example, to add a (nx1) column vector to a (1xm) row vector and obtain an (nxm) matrix (which we cannot do at present, we need ".+" for that). Riccardo (Jack) Lucchetti Dipartimento di Economia Università Politecnica delle Marche r.lucchetti(a)univpm.it http://www.econ.univpm.it/lucchetti