Using my 5 year old 533mhz Mac with 640mb ram (very sloooooow) and J5.04 the differences are much more dramatic, as well as slow. Btw, the space usage differential is greater for the last two tests, also.
ts 'D=:10000000$d' NB. reference timing 0.39102 6.71098e7 ts'((1:,2:>/\]);@(<&(<./\);. 1)])D' 83.27 5.08264e8 ts'((1:,}:>}.);@(<&(<./\);. 1)])D' 32.0341 5.08263e8 ts '(}.>}:)D' 0.988776 1.50996e8 ts '(2: >/\ ])D' 29.152 2.18106e8 (B=) On Fri, 24 Mar 2006, John Randall wrote: + There is definitely an OS difference. I have a dual-boot (XP and Linux) + laptop with 1G memory rated at 1.59 GHz. Using R.E. Boss's timing code I + get + + Windows XP Professional + + ts 'D=:10000000$d' NB. reference timing + 0.102902 6.71098e7 + ts'((1,2>/\]);@(<&(<./\);. 1)])D' + 0.352682 8.38894e7 + ts'((1,}:>}.);@(<&(<./\);. 1)])D' + 0.42031 1.50998e8 + ts '(}.>}:)D' + 0.283239 1.50996e8 + ts '(2: >/\ ])D' + 0.223209 1.67792e7 + + Linux Fedora Core 4 + + ts 'D=:10000000$d' NB. reference timing + 0.082827 6.71098e7 + ts'((1,2>/\]);@(<&(<./\);. 1)])D' + 0.88911 8.38894e7 + ts'((1,}:>}.);@(<&(<./\);. 1)])D' + 0.680525 1.50998e8 + ts '(}.>}:)D' + 0.36968 1.50996e8 + ts '(2: >/\ ])D' + 0.597623 1.67792e7 + + It appears that the Windows implementation favors 2>/\] while the Linux + implementation favors }.>}:, and the Windows version is generally faster. + + Anyone have any ideas why this should be so? + + Best wishes, + + John + + + + Mike Day wrote: + > Getting off topic; perhaps differences in machine/OS + > are to blame? I'm running Windows XP Home Professional + > on a 512 Mb PC with 1 Pentium 4 rated at 2.66GHz ... + > + > Anyway, as I said earlier, there's not much to choose + > between the idioms, and as John Randall says, it's + > easier to remember the old one, at least for me! + > + > Mike + > + > R.E. Boss wrote: + > + >>I cannot confirm the performance figures of Day: + >> ts 'D=:10000000$d' NB. reference timing + >>0.0505433 6.71098e7 + >> + >> ts'((1,2>/\]);@(<&(<./\);. 1)])D' + >>0.203427 8.38894e7 + >> ts'((1,}:>}.);@(<&(<./\);. 1)])D' + >>0.215576 1.50998e8 + >> + >>neither detect much difference in performance in: + >> ts '(}.>}:)D' + >>0.142718 1.50996e8 + >> ts '(2: >/\ ])D' + >>0.146728 1.67792e7 + >> + >>R.E. Boss + >> + >>-----Oorspronkelijk bericht----- + >>Van: [EMAIL PROTECTED] + >>[mailto:[EMAIL PROTECTED] Namens John Randall + >>Verzonden: vrijdag 24 maart 2006 13:54 + >>Aan: Programming forum + >>Onderwerp: Re: [Jprogramming] Closest local minimums of data + >> + >>I am aware of 2 >/\ ], but I tend to use }:>}. for prototyping and small + >>arrays, since I can accurately read and write it without looking anything + >>up. Of course there is a performance penalty for large arrays, since + >>}:>}. must create two intermediate arrays of size n-1 as well as the + >>result. + >> + >>Best wishes, + >> + >>John + >> + >>Mike Day wrote: + >> + >> + >>>As you noted, John Randall's }: > }. is of interest. + >>>2 >/\ ] is a natural J/APL2 way to do it, whereas }: > }. is the J + >>>form of an ancient APL1 idiom for first differences and the like, + >>>and seems faster for smallish d, but loses out for your required + >>>size of vector for space requirement. However, the performance + >>>is pretty good with either idiom. + >>> + >>> ts =: 6!:2 , 7!:[EMAIL PROTECTED] NB. time & space + >>> + >>> D=:10000$d NB. "old" method faster + >>> ts'((1,2>/\]);@(<&(<./\);. 1)])D ' + >>>0.000238578 85248 + >>> ts'((1,}:>}.);@(<&(<./\);. 1)])D ' + >>>0.000155048 150464 + >>> + >>> D=:50000$d NB. both similar for time + >>> ts'((1,2>/\]);@(<&(<./\);. 1)])D ' + >>>0.00151164 331008 + >>> ts'((1,}:>}.);@(<&(<./\);. 1)])D ' + >>>0.00151807 592832 + >>> + >>> D=:100000$d NB. "new" method faster + >>> ts'((1,2>/\]);@(<&(<./\);. 1)])D NB. tacit form' + >>>0.00302441 658688 + >>> ts'((1,}:>}.);@(<&(<./\);. 1)])D NB. tacit form' + >>>0.00445364 1.18266e6 + >>> + >>>Mike + >>> + >>> + >>>Mikl Kurkov wrote: + >>> + >>> + >>> + >>>>On Fri, 24 Mar 2006 02:43:00 +0300, Mike Day + >>>><[EMAIL PROTECTED]> wrote: + >>>> + >>>> + >>>> + >>>>>I was drafting this before Oleg's reply arrived. It's slightly + >>>>>different from his, and shows a derivation of a tacit form. + >>>>>============================================================== + >>>>>Is this the sort of thing you need? Consider: + >>>>> + >>>>> + >>>>Yes, exactly. + >>>> + >>>> + >>>> + >>>>> d + >>>>>10 7 5 6 7 1 9 8 2 4 + >>>>> (1 , 2 >/\ ])d NB. boolean for = left > right for each pair ? + >>>>>1 1 1 0 0 1 0 1 1 0 + >>>>> + >>>>> 1 1 1 0 0 1 0 1 1 0 < ;. 1 d NB. partition d by this boolean + >>>>>+--+-+-----+---+-+---+ + >>>>>|10|7|5 6 7|1 9|8|2 4| + >>>>>+--+-+-----+---+-+---+ + >>>>> 1 1 1 0 0 1 0 1 1 0(<&(<./\);. 1)d NB. required work in boxes + >>>>>+--+-+-----+---+-+---+ + >>>>>|10|7|5 5 5|1 1|8|2 2| + >>>>>+--+-+-----+---+-+---+ + >>>>> + >>>>> 1 1 1 0 0 1 0 1 1 0 ;@(<&(<./\);. 1)d NB. unbox + >>>>>10 7 5 5 5 1 1 8 2 2 + >>>>> + >>>>> ((1,2>/\]);@(<&(<./\);. 1)])d NB. tacit form + >>>>>10 7 5 5 5 1 1 8 2 2 + >>>>> + >>>>> (;@(<&(<./\);. 1)~1,2>/\])d NB. tacit avoiding one "]" 10 7 5 5 5 + >>>>>1 1 8 2 2 + >>>>> + >>>>>Mike + >>>>> + >>>>> + >>>>Thanks for explanations. Your version seems to be most efficient. + >>>> + >>>> + >>>> + >>>---------------------------------------------------------------------- + >>>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 + > + + + ---------------------------------------------------------------------- + For information about J forums see http://www.jsoftware.com/forums.htm + (B=) <----------my "sig" Brian Schott Atlanta, GA, USA schott DOT bee are eye eh en AT gee em ae eye el DOT com http://schott.selfip.net/~brian/ ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
