Timing is not everything. In this case f2 is computing something weird and possibly misleading: All the elements of a row are the same. e.g.
f2 3 4$9 2.06843 2.06843 2.06843 2.06843 5.20443 5.20443 5.20443 5.20443 1.00311 1.00311 1.00311 1.00311 f3 3 4$9 3.36383 8.62184 6.76132 4.76392 8.01329 7.10008 0.285073 3.84514 0.950537 6.16313 0.214141 3.56592 ----- Original Message ----- From: "R.E. Boss" <[EMAIL PROTECTED]> Date: Monday, June 30, 2008 23:56 Subject: RE: [Jprogramming] Random number generation To: 'Programming forum' <[email protected]> > f3=: 3 : 'y * ($y) [EMAIL PROTECTED] 0' > f2=: 3 : 'y * ?(#y)#0' > > ts 'f2 Y' [Y=:1000 1000$9 > 0.0098060407 8402944 > ts 'f3 Y' > 0.034617353 16781696 > > > R.E. Boss > > > > -----Oorspronkelijk bericht----- > > Van: [EMAIL PROTECTED] [mailto:programming- > > [EMAIL PROTECTED] Namens Joey K Tuttle > > Verzonden: maandag 30 juni 2008 19:41 > > Aan: Programming forum > > Onderwerp: Re: [Jprogramming] Random number generation > > > > Interestingly, I see almost no change in speed/space between > (my) f2 and > > f3... > > > > ts 'f2 1000 1000$9' > > 0.231313 2.20224e7 > > ts 'f3 1000 1000$9' > > 0.235067 2.0974e7 > > > > Well - I guess a million bytes in space saving is > > nothing to sneeze at (used to be a lot of > > memory...) so I applaud the optimization work you > > have done! > > > > Thanks - joey > > > > At 10:08 -0700 2008/06/30, Roger Hui wrote: > > >To gain more speed (and reduce space), use: > > > > > >f3=: 3 : 'y * ($y) [EMAIL PROTECTED] 0' > > > > > >[EMAIL PROTECTED] is supported by special code. The difference > > >is most striking for random booleans: > > > > > > ts=: 6!:2 , 7!:[EMAIL PROTECTED] > > > > > > ts '1e6 [EMAIL PROTECTED] 2' > > >0.00275063 1.04934e6 > > > ts '?1e6$2' > > >0.00555685 5.24352e6 > > > > > > > > > > > >----- Original Message ----- > > >From: Joey K Tuttle <[EMAIL PROTECTED]> > > >Date: Monday, June 30, 2008 8:54 > > >Subject: RE: [Jprogramming] Random number generation > > >To: Programming forum <[email protected]> > > >Cc: 'Programming forum' <[email protected]> > > > > > >> Not to quibble... but > > >> > > >> f2 =: 3 : 'y * ?(#y)#0' > > >> > > >> has a related trouble to the original post with > > >> argument rank > 1 ... f1 is actually better in > > >> extending "to work with arrays of any shape". To > > >> try to gain some speed, perhaps you really meant > > >> to say: > > >> > > >> f2 =: 3 : 'y * ?($y)$0' > > >> > > >> - joey > > >> > > >> > > >> At 10:59 -0400 2008/06/30, Henry Rich wrote: > > >> >What you executed was: > > >> > > > >> >3 3 * ?0 > > >> > > > >> >which is > > >> > > > >> >3 3 * (?0) > > >> > > > >> >in other words, you asked for one number, then > multiplied it by > > >> 3 twice. > > >> > > > >> > > > >> >You could have your verb apply to atoms by giving it > a rank of 0: > > >> > > > >> > f1 =: 3 : 'y * ?0'"0 > > >> > > > >> >Or, you could design it to work with arrays of any shape: > > >> > > > >> > f2 =: 3 : 'y * ?(#y)#0' > > >> > > > >> >Working with bigger arrays is faster, but perhaps > not by enough > > >> >to be worth the trouble. Depends on your > application.> >> > > > >> >Henry Rich > > >> > > > >> > > > >> >> -----Original Message----- > > >> >> From: [EMAIL PROTECTED] > > >> >> [mailto:[EMAIL PROTECTED] > On Behalf Of > > >> >> Benoît Roesslinger > > >> >> Sent: Monday, June 30, 2008 10:46 AM > > >> >> To: [email protected] > > >> >> Subject: [Jprogramming] Random number generation > > >> >> > > >> >> Hi, > > >> >> > > >> >> I am new to J and when doing some > experiments with random > > >> >> number generation > > >> >> I stumbled across the following behavior, > which wasn't what > > >> >> I'd expect : > > >> >> > > >> >> f=: 3 : 'y * ?0' > > >> >> f 3 > > >> >> 2.91414 > > >> >> f 3 > > >> >> 0.139888 > > >> >> f 3 > > >> >> 0.990328 > > >> >> > > >> >> OK so far, but when I tried: > > >> >> > > >> >> f 3 3 > > >> >> > > >> >> it gives me : > > >> >> > > >> >> 0.0403801 0.0403801 (same values!) > > >> >> > > >> >> whereas I'd expect a behavior much like the > one of '?'... > > >> >> Is this behavior normal ? > > >> >> Suppose I want to create a function to > generate a random > > >> >> deviate from a > > >> >> distribution (normal for instance) with some > parameters (mean > > >> >> and sd for > > >> >> instance) that will work in the same fashion > as '?', ie > > >> it is > > >> >> possible to > > >> >> generate lots of random deviates at once > using code > > >> such as : > > >> >> distri 100 $ > > >> >> x, where x would represent parameters, what > is the best > > >> way to go ? > > >> >> > > >> >> Many thanks in advance! > > >> >> > > >> >> Benoît. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
