[Jprogramming] J weirdness #2 - A nasty surprise

['Pascal Jasmin' via Programming]

You can copy beta to a new directory and run each independently.





________________________________
From: Michael Goodrich <michael.goodrich at gmail.com>
To: programming at jsoftware.com 
Sent: Monday, April 17, 2017 5:14 PM
Subject: Re: [Jprogramming] J weirdness #2 - A nasty surprise



This is getting interesting; I was already impressed with Js speed being only twice as slow as the C version, and faster than the R version of the same code.

Looking forward to that 806 beta 3!

Btw I should uninstall the latest (stable) and start afresh?


Sent from my iPhone

> On Apr 17, 2017, at 5:03 PM, Raul Miller <rauldmiller at gmail.com> wrote:
> 
> I think you were surprised by
> http://www.jsoftware.com/help/dictionary/special.htm
> 
> Specifically the special handling for +/ .* (which is handled at
> parsing time rather than at execution time - the way you have things
> arranged, the parser will not see +/ .* and hypothetically you could
> arrange for sum .* in contexts where sum was defined differently).
> 
> I hope this helps,
> 
> -- 
> Raul
> 
> 
> On Mon, Apr 17, 2017 at 4:51 PM, Michael Goodrich
> <michael.goodrich at gmail.com> wrote:
>> Greetings:
>> 
>> Got a nasty surprise today.  have a non-trivial J app with the following
>> supporting original definitions:
>> 
>> sum =. +/
>> dot =. +/ . *
>> sqrd =. *:
>> ssq =. +/ @: sqrd
>> 
>> 
>> Which I changed (thinking I was being elegant) to
>> 
>> sum =. +/
>> dot =. sum . *
>> sqrd =. *:
>> ssq =. sum @: sqrd
>> 
>> After this change the run time increased by a factor of 5!
>> 
>> Insights?
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm

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