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.
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