[R] x*x*x*... vs x^n

[Robin Hankin]

On Jun 29, 2005, at 02:47 pm, Duncan Murdoch wrote:

> On 6/29/2005 9:31 AM, Robin Hankin wrote:
>
>> Hi  Duncan
>>
>>
>> library(gsl)
>> system.time(ignore <- pow_int(a,8))
>> [1] 1.07 1.11 3.08 0.00 0.00
>>
>> <why the slow execution time?>
>>
>
> Shouldn't you ask the gsl maintainer that? :-)
>

well  I did ask myself, but  in this case the gsl maintainer
told me to ask the gsl co-author, who
is no doubt much better informed in these matters ;-)

>>
>> (Of course, I'm not suggesting that other programming tasks be
>> suspended!  All I'm pointing
>> out is that there may exist a user to whom fast integer powers are
>> very very important)
>>
>
> Then that user should submit the patch, not you.  But whoever does it
> should include an argument to convince an R core member that the  
> change
> is worth looking at, and do it well enough that the patch is accepted.
> Changes to the way R does arithmetic affect everyone, so they had  
> better
> be done right, and checking them takes time.
>

yes, that's a fair point.
But including a native R command pow.int(), say, wouldn't  affect  
anyone, would it?
One could even use the (tested) GSL code, as it is GPL'ed.

This would just be a new function that users could use at their  
discretion, and no
existing code would break.

I assume that such a function would  not suffer whatever performance  
disadvantage
that the GSL package approach had, so it may well be quite a  
significant improvement
over the method used by R_pow_di() in arithmetic.c especially for  
large n.


best wishes

rksh

> Duncan Murdoch
>
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