Perhaps we have both been missing the point. I hastily said “you won’t be able to ‘matrix multiply gerund matrices’”
In J, you can actually achieve that. And if that’s what OP wanted, we indeed missed the point. A solution would then keep R as-is in order to let the user make good use of Js functional algebra/grammar (but beware of any verbs that don’t have rank 0). When it comes to evaluating a matrix of this kind, I don’t see a necessity to alter OP’s solution other than making it an adverb (maybe a matter of taste). Then R mf pi%4 would work without parenthesis. Looking forward to replies from other members of this list. And thanks to Ben: I didn’t know one can use both r and p in a single numeric literal. I’ll have to study microsyntax again. cheers, Hauke Am 18.12.20 um 12:56 schrieb Ben Gorte: > Perhaps I'm missing the point, but I would say: > > R =: ((cos , -@sin) ,: sin , cos) > > R 1r6p1 > > 0.866025 _0.5 > > 0.5 0.866025 > > > Ben > > On Fri, 18 Dec 2020 at 18:59, Francesco Pedulla' <mel...@gmail.com> wrote: > >> Dear all, >> I need to represent the 2D rotation matrix 'R' >> >> R = |cos(t) -sin(t)| >> |sin(t) cos(t)| >> >> and compute it for different values of the rotation angle 't'. I am aware >> the matrix of function can be represented as a gerund, which I like: >> >> R =: 2 2$cos`(-@sin)`sin`cos . >> >> To compute R(t), I wrote the following definition: >> >> mf =: conjunction : '($x)$,(,x)/.((+/$x)$y)' >> >> >> so that "R mf pi%4" returns R(pi/4). But I find the code for 'mf' not very >> elegant. Is there a better way to achieve this? >> Thanks in advance for any hint, >> >> Francesco >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > -- ---------------------- mail written using NEO neo-layout.org ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
