Re: Slowdown
- To: mathgroup at smc.vnet.net
- Subject: [mg53241] Re: Slowdown
- From: Roland Franzius <roland.franzius at uos.de>
- Date: Sun, 2 Jan 2005 04:12:50 -0500 (EST)
- Organization: Universitaet Hannover
- References: <cr33tt$je6$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Maxim wrote:
> Consider:
>
> In[1]:=
> Module[{f, L},
> L = f[];
> Do[L = f[L, i], {i, 10^4}]
> ] // Timing
>
> Module[{weirdness, L},
> L = weirdness[];
> Do[L = weirdness[L, i], {i, 10^4}]
> ] // Timing
>
> Out[1]=
> {0.015*Second, Null}
>
> Out[2]=
> {3.063*Second, Null}
>
> Here the timings differ by a factor of 200. Besides, the timing grows
> linearly in the first case and quadratically in the second (therefore, for
> n=10^5 there will be an approximately 2000 times slowdown). We can only
> guess that something goes wrong with the symbol name hashing.
The timing difference occurs when the symbol "wierdness" exceeds 8
characters. Test it for "wierdnes". That seems to be a consequence of
the machine routine for string comparison. Up to 8 characters can be
used without using a memory to memory compare. Of course it should be
possible to write a compare routine that makes not such a bit step.
--
Roland Franzius
- Follow-Ups:
- Re: Re: Slowdown
- From: yehuda ben-shimol <benshimo@bgu.ac.il>
- Re: Re: Slowdown