Dear GAP Forum,
Marek Mitros asked:
>
> I am trying to use the cvec package to have compressed matrices over GF(2).
> But I do not see much difference - see below example log from my GAP
> session.
>
This isn’t really surprising. GAP already supports compressed matrices over
fields of order up to 256. The cvec package does not achieve more compression
for these fields, but (a) may have faster methods for some operations and/or a
better interface and (b) also supports space and time efficient arithmetic for
larger fields.
In your particular case, the matrices have roughly 19 million entries and the
memory usages you report are not much over 19 million bits, so there is not
much saving to be had.
Steve
>
> gap> g:=AtlasGroup("B"); Print("Baby defined\n");
>
> <matrix group of size 4154781481226426191177580544000000 with 2 generators>
>
> Baby defined
>
> gap> ge:=GeneratorsOfGroup(g); a:=ge[1]; b:=ge[2];
>
> [ <an immutable 4370x4370 matrix over GF2>, <an immutable 4370x4370 matrix
> over GF2> ]
>
> <an immutable 4370x4370 matrix over GF2>
>
> <an immutable 4370x4370 matrix over GF2>
>
> gap>
>
> gap> LoadPackage("cvec"); # compressed vectors and matrices over finite
> fields
>
> true
>
> gap> ca:=CMat(a); cb:=CMat(b);
>
> <cmat 4370x4370 over GF(2,1)>
>
> <cmat 4370x4370 over GF(2,1)>
>
> gap>
>
> gap> MemoryUsage(a);
>
> 2519320
>
> gap> MemoryUsage(ca);
>
> 2500728
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