You probably meant to use parenthesis, instead of using dyadic rank 1
5 for your summation?
Thanks,
--
Raul
P.S.
+/("1) 5{.TST
3 12 21 30 39
On Sat, Mar 14, 2015 at 6:59 AM, Linda Alvord <[email protected]> wrote:
> Why isn't the final line 3 12 21 30 39
>
>
>
> (i.5){TST=: i. 2e6 3
>
> 0 1 2
>
> 3 4 5
>
> 6 7 8
>
> 9 10 11
>
> 12 13 14
>
> $TST
>
> 2000000 3
>
> (i.5){(0&{"1 + 1&{"1 + 2&{"1) TST
>
> 3 12 21 30 39
>
> (i.5){+/"1 TST
>
> 3 12 21 30 39
>
> 5{.TST
>
> 0 1 2
>
> 3 4 5
>
> 6 7 8
>
> 9 10 11
>
> 12 13 14
>
> +/"1 5{.TST
>
> 3
>
>
>
> Linda
>
>
>
>
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Tikkanz
> Sent: Friday, March 13, 2015 9:27 PM
> To: Programming JForum
> Subject: [Jprogramming] Performance query
>
>
>
> I noticed some interesting behaviour when trying to simplify a J sentence.
>
> The simple J-like solution was slower than the more complex proscriptive
> one.
>
>
>
> Given an array:
>
> TST=: i. 2e6 3
>
>
>
> To sum the columns with each other (i.e. sum the rows), I can
>
> a) extract each column and the lists together:
>
>
>
> (0&{"1 + 1&{"1 + 2&{"1) TST
>
>
>
> b) sum the items in each row
>
>
>
> +/"1 TST
>
>
>
> Sentences a) and b) are equivalent:
>
> (+/"1 -: (0&{"1 + 1&{"1 + 2&{"1)) TST
>
> 1
>
>
>
> And as I expected, the simpler sentence is faster and leaner.
>
> 10 timespacex '(0&{"1 + 1&{"1 + 2&{"1) TST'
>
> 0.0439944 5.03372e7
>
> 10 timespacex '+/"1 TST'
>
> 0.0138071 1.67798e7
>
>
>
> If I use GCD instead of Plus, the approaches are still equivalent, but the
> simpler sentence is much slower (while still being leaner).
>
> (+./"1 -: 0&{"1 +. 1&{"1 +. 2&{"1) TST
>
> 1
>
> 10 timespacex '(0&{"1 +. 1&{"1 +. 2&{"1) TST'
>
> 0.132607 5.03372e7
>
> 10 timespacex '+./"1 TST'
>
> 0.943093 1.67805e7
>
>
>
> Is this to be expected because of differences in the nature of the GCD and
> Plus operations, or does it reflect an opportunity for future optimisation
> of ( +. ) ?
>
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>
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