Re: [Gcl-devel] [Maxima] use_fast_arrays is slow in GCL for hash tables

[Camm Maguire]

Greetings, and thanks for pointing this out!  

As you might suspect, this is a weakness in the hash function algorithm
for this set of keys, which is currently generating too many collisions.

I've committed a fix into the stable and experimental branches which you
might like to look at.  Am also updating the appropriate Debian
packages.

Take care,

Barton Willis <address@hidden> writes:

> Assign and access  a 40,000 member hashtable
>
>   GCL: 100.6400 seconds
>   CCL:     0.7800 seconds
>
> This has been pointed out before, I think. The code:
>
> (%i1) showtime : true$
> Evaluation took 0.0000 seconds (0.0000 elapsed)
> (%i2) block([use_fast_arrays : true, n : 200],
>   (for i : 1 thru n do for j : 1 thru n do a[i,j] : i+j,
>    s : 0,
>    for i : 1 thru n do for j : 1 thru n do s : s + a[i,j]));
> Evaluation took 100.6400 seconds (100.6400 elapsed)
> (%o2) done
>
> (%i3) s;
> Evaluation took 0.0000 seconds (0.0000 elapsed)
> (%o3) 8040000
> (%i4) block([use_fast_arrays : false, n : 200],
>   (for i : 1 thru n do for j : 1 thru n do b[i,j] : i+j,
>    s : 0,
>    for i : 1 thru n do for j : 1 thru n do s : s + b[i,j]));
> Evaluation took 0.7700 seconds (0.7700 elapsed)
> (%o4) done
> (%i5) s;
> Evaluation took 0.0000 seconds (0.0000 elapsed)
> (%o5) 8040000
>
>
> With CCL:
>
> (%i1) showtime : true$
> Evaluation took 0.0000 seconds (0.0000 elapsed)
> (%i2) block([use_fast_arrays : true, n : 200],
>   (for i : 1 thru n do for j : 1 thru n do a[i,j] : i+j,
>    s : 0,
>    for i : 1 thru n do for j : 1 thru n do s : s + a[i,j]));
> Evaluation took 0.7800 seconds (0.7800 elapsed)
> (%o2)                                done
> (%i3) s;
> Evaluation took 0.0000 seconds (0.0000 elapsed)
> (%o3)                               8040000
> (%i4) block([use_fast_arrays : false, n : 200],
>   (for i : 1 thru n do for j : 1 thru n do b[i,j] : i+j,
>    s : 0,
>    for i : 1 thru n do for j : 1 thru n do s : s + b[i,j]));
> Evaluation took 0.8892 seconds (0.8900 elapsed)
> (%o4)                                done
> (%i5) s;
> Evaluation took 0.0000 seconds (0.0000 elapsed)
> (%o5)                               8040000
> (%i6)
>
>
>
>
> --Barton
>
> _______________________________________________
> Maxima mailing list
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> http://www.math.utexas.edu/mailman/listinfo/maxima
>
>
>
>

-- 
Camm Maguire                                        address@hidden
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"The earth is but one country, and mankind its citizens."  --  Baha'u'llah