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Error with LowIndexNormalSubs : Large Indexes #66

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guillde opened this issue Sep 23, 2024 · 1 comment · May be fixed by #67
Open

Error with LowIndexNormalSubs : Large Indexes #66

guillde opened this issue Sep 23, 2024 · 1 comment · May be fixed by #67

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@guillde
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guillde commented Sep 23, 2024

For sufficiently large indexes, LowIndexNormalSubs will throw the error below. If I run, for example:

f := FreeGroup("a", "b", "c");;
a:= f.1;; b := f.2;; c := f.3;;
g := f / [a^2, b^2, c^2, (a*b)^(4), (b*c)^(4), (c*a)^(4)]; 

l := LowIndexNormalSubs(g,10000);

I get the following error:

Error, List Elements: <list>[1025] must have an assigned value in
qs!.images{generators} := gens{[ 1 .. d ]}; at /.../lib/pquot.gi:1352 called from
AbelianPQuotient( qs ); at  /.../lib/pquot.gi:1463 called from
PQuotient( IH, p, 1, LINS_MaxPGenerators ) at /.../LINS/gap/findPQuotients.gi:275 called from
LINS_FindPModules( gr, rK, p, opts ); at /.../LINS/gap/findPQuotients.gi:354 called from
LINS_FindPModules( gr, rK, p, opts ); at  /.../LINS/gap/findPQuotients.gi:354 called from
LINS_FindPModules( gr, rK, p, opts ); at /.../LINS/gap/findPQuotients.gi:354 called from
...  at test.g:7
type 'quit;' to quit to outer loop

I have tried this for some Coexter groups. This is for LINS 0.9.
@FriedrichRober
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Thanks for the bug report. The error seems to result from the internal parameter LINS_MaxPGenerators being too low for your specific example. I think setting this parameter to the index that you search for should fix the error.

As a quick dirty fix, I hope the following will work:

MakeReadWriteGlobal("LINS_MaxPGenerators");
LINS_MaxPGenerators := 10000;;
l := LowIndexNormalSubs(g,10000);

It will take a few days until I have time to make a proper fix.

@FriedrichRober FriedrichRober linked a pull request Oct 9, 2024 that will close this issue
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Fix bug caused by LINS_MaxPGenerators being too low. gap-packages/LINS
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@guillde @FriedrichRober