Some fine tuning of your original ffrom makes it almost as fast as ffrom2:
ff=: 4 : 0
b =. #:i.2^#x
p =. <.x
+/(*/(|: b){"_1 (-.,.])x-p) * (<"1 p +"1 b) { y
)
Notice that I don't use a boxed LHA (as I did for ffrom & ffrom2).
L=.0.9*,"0/~i.n [ R=.i.,~n=.100
L (ffrom"1 _ -: ff"1 _) R
1
([: 5&ts 'L ', ' R',~]) &.> 'ffrom2"1 _'; 'ff"1 _'; 'ffrom"1 _'
┌──────────────┬───────────────┬───────────────┐
│0.45198 202112│0.466671 203328│0.574397 204288│
└──────────────┴───────────────┴───────────────┘
Hallo Ben Gorte - LR, je schreef op 24-01-11 19:21:
> Aha! your version from Yesterday (without loops) is really the fastest
> one!
> It remains my favorite ffrom.
>
> ffrom=:4 :0 "0 _
> x=.,>x
> range=. { (<.,>.)&.> x
> mult=. *// (,.~-.) (-<.) x
> mult +/^:(#x)@:* range{y
> )
>
> 6!:2 '((<"1)0.9*,"0/~i.n)ffrom2 i.n,n=.100'
> 0.223896
> 6!:2 '((<"1)0.9*,"0/~i.n)ffrom2 i.n,n=.200'
> 0.893405
>
> Ben
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Ben Gorte - LR
> Sent: maandag 24 januari 2011 18:42
> To: Programming forum
> Subject: Re: [Jprogramming] Floating from
>
> If it is about speed (not beauty), then it seems yours is not very fast
> when selecting a lot of elements at once, as in bilinear image
> resampling.
>
> The example:
>
> ((<"1)0.9*,"0/~i.n)ffrom2 i.n,n=.5
> 0 0.9 1.8 2.7 3.6
> 4.5 5.4 6.3 7.2 8.1
> 9 9.9 10.8 11.7 12.6
> 13.5 14.4 15.3 16.2 17.1
> 18 18.9 19.8 20.7 21.6
>
> This is your fastest version:
>
> 6!:2 '((<"1)0.9*,"0/~i.n)ffrom2 i.n,n=.100'
> 0.405595
> 6!:2 '((<"1)0.9*,"0/~i.n)ffrom2 i.n,n=.200'
> 6.26634
>
> About mine I may say:
>
> 6!:2 '((<"1)0.9*,"0/~i.n) bgffrom i.n,n=.100'
> 0.27029
> 6!:2 '((<"1)0.9*,"0/~i.n) bgffrom i.n,n=.200'
> 1.07775
>
> (pure luck, I admit)
>
> Ben
>
>
>
>
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Marshall
> Lochbaum
> Sent: maandag 24 januari 2011 14:06
> To: 'Programming forum'
> Subject: Re: [Jprogramming] Floating from
>
> If you want one that works exactly like the others, replace }. in the
> code with |. . This is a much more elegant way to do it, but it
> requires moving the whole array around and more time and space (it is
> about three times slower).
>
> Marshall
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Ben Gorte - LR
> Sent: Monday, January 24, 2011 2:14 AM
> To: Programming forum
> Subject: Re: [Jprogramming] Floating from
>
> Impressed again.
> I suppose I should start using that one in my application,
>
> However you were changing the specs.
> Your previous one is the real ffrom.
>
> Ben
>
>
> -----Original Message-----
> From: [email protected] on behalf of Marshall Lochbaum
> Sent: Mon 1/24/2011 1:18 AM
> To: 'Programming forum'
> Subject: Re: [Jprogramming] Floating from
>
> I have a better version!
> This one, despite an ugly for loop, uses more J array power and
> outperforms my previous attempt by an order of magnitude in time and
> space.
>
> ffrom=:4 :0"0 _
> x=.,>x
> a=.(2"0 x) {. (<.x) }. y
> mult=. (,.~-.) (-<.) x
> for_m. mult do.
> a=. m +/@:* a
> end.
> a
> )
> 6!:2 '(<?20$0) ffrom i.20#2'
> 0.0627697
> 7!:2 '(<?20$0) ffrom i.20#2'
> 75506048
>
> Note that this one, because of its use of head, substitutes 0 for any
> value that is out of range. It also doesn't work for negative indices.
>
> Marshall
>
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