Oops, I thought I had included that. But it looks like one of my formatting edits lost it.

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inds=: I. @ (+./ .*.) Thanks, -- Raul On Wed, Oct 12, 2016 at 10:00 PM, Michal Dobrogost < michal.dobrog...@gmail.com> wrote: > Hi Raul, > > What is the definition of *inds*? > > I would describe the higher level operation as: select the rows of Y where > X is 1. Then take the column-wise OR of them. > > However the real thing I'm interested in is generating the lookup tables > which serve as an intermediate step in the higher level operation. > > On Wed, Oct 12, 2016 at 9:35 AM, Raul Miller <rauldmil...@gmail.com> > wrote: > > > I'm not quite sure I understand what you are doing here. > > > > Here's what I understand from your description: > > > > You're looking for rows where a bit set in X has a bit set in Y, and > > you want to split up X and Y into smaller pieces for your intermediate > > result, and you want to use indices rather than bit operations for > > your final operation. > > > > That gives me something like this. > > > > X =: ? 5 $ 2 > > Y =: 30 > ? 5 6 $ 100 > > X > > 0 1 1 1 1 > > Y > > 0 0 0 0 0 0 > > 1 0 0 0 0 0 > > 1 1 1 0 0 1 > > 1 0 0 1 0 0 > > 0 0 0 0 0 1 > > (_2 {. X) inds _2 {. Y > > 0 3 5 > > (3 {. X) inds 3 {. Y > > 0 1 2 5 > > 0 3 5 ([ -. -.) 0 1 2 5 > > 0 5 > > > > So maybe you would be looking at making an adverb along the lines of: > > > > L=: adverb define > > : > > (m {. x) inds m {. y > > ) > > > > Or, more concisely: > > > > L=: adverb define > > inds&(m&{.) > > ) > > > > But when I look at your calculations, I don't see anything like this. > > > > If I am off base here, could you describe how what you are looking for > > differs from what I am understanding? > > > > Thanks, > > > > -- > > Raul > > > > > > On Wed, Oct 12, 2016 at 12:14 PM, Michal Dobrogost > > <michal.dobrog...@gmail.com> wrote: > > > Hi All, > > > > > > I've been mucking around generating look up tables in C++. Getting > > > frustrated, I wrote up this J single liner. Can you think of ways to > > > simplify the LUT computation (the expression we assign to L2 and L3 > > below)? > > > > > > *Original Operator (no LUT)* > > > > > > ] x =. ? 5 $ 2 > > > 1 0 1 1 0 > > > ] y =. 30 > ? 5 6 $ 100 > > > 1 0 0 0 0 0 > > > 0 1 0 1 1 0 > > > 0 1 0 0 0 1 > > > 0 0 0 0 1 1 > > > 0 1 1 1 0 1 > > > x (+./@:*.) y > > > 1 1 0 0 1 1 > > > > > > *LUT Explanation* > > > > > > The idea is to break up x into smaller chunks (2-bits, 3-bits, etc) and > > > precompute the operation for the corresponding chunks of y. Then we > just > > > convert the chunks into indices and look them up in the LUT. > > > > > > _2<\x > > > ┌───┬───┬─┐ > > > │1 0│1 1│0│ > > > └───┴───┴─┘ > > > _2#.\x > > > 2 3 0 > > > > > > *2-bit LUT* > > > > > > ]L2=. _2((#:@:i.@:(2&^)@:#) (+./"2 @: (*."0 1"1 _)) ])\y > > > 0 0 0 0 0 0 > > > 0 1 0 1 1 0 > > > 1 0 0 0 0 0 > > > 1 1 0 1 1 0 > > > > > > 0 0 0 0 0 0 > > > 0 0 0 0 1 1 > > > 0 1 0 0 0 1 > > > 0 1 0 0 1 1 > > > > > > 0 0 0 0 0 0 > > > 0 1 1 1 0 1 > > > 0 0 0 0 0 0 > > > 0 0 0 0 0 0 > > > > > > +./ (_2#.\x) {"0 2 L2 NB. Compute by 2-bit lookups > > > 1 1 0 0 1 1 > > > > > > *3-Bit LUT* > > > > > > ]L3=. _3((#:@:i.@:(2&^)@:#) (+./"2 @: (*."0 1"1 _)) ])\y > > > 0 0 0 0 0 0 > > > 0 1 0 0 0 1 > > > 0 1 0 1 1 0 > > > 0 1 0 1 1 1 > > > 1 0 0 0 0 0 > > > 1 1 0 0 0 1 > > > 1 1 0 1 1 0 > > > 1 1 0 1 1 1 > > > > > > 0 0 0 0 0 0 > > > 0 1 1 1 0 1 > > > 0 0 0 0 1 1 > > > 0 1 1 1 1 1 > > > 0 0 0 0 0 0 > > > 0 0 0 0 0 0 > > > 0 0 0 0 0 0 > > > 0 0 0 0 0 0 > > > > > > +./ (_3#.\x) {"0 2 L3 NB. Compute by 3-bit lookups > > > 1 1 0 0 1 1 > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm