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Add constructive recognition of SL(2,q) in natural representation 2.0 #398

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Merged
fingolfin merged 21 commits into from
Apr 30, 2026
Merged

Add constructive recognition of SL(2,q) in natural representation 2.0 #398

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93299cd
Add Frank Lübeck's SL2 natural representation recognition 2.0
Mar 19, 2026
4a496a8
load sl2_natural.gi in read.g
Mar 21, 2026
e316a83
add test for ConRecogNaturalSL2
Mar 21, 2026
ed208f9
Add RECOG.ConRecogNaturalSL22 for constructive recognition of SL(2,2)
Mar 21, 2026
9d61f0a
Add test for RECOG.ConRecogNaturalSL22 in sl2.tst
Mar 21, 2026
113126c
using explicit SL22 function
Mar 24, 2026
6e869b3
Require GAP >=4.13 and remove 4.12 from CI
Mar 24, 2026
8d54b9a
Restore contrib/frank/sl2
Mar 25, 2026
795b6aa
Add function ConRecogNaturalSL25 for SL(2,5) and tests
Mar 25, 2026
2938a37
recog: improve ConRecogNaturalSL25
Mar 30, 2026
4924c93
recog: add ConRecogNaturalSL23 for SL(2,3)
Mar 31, 2026
023eb93
Fix RECOG.RecogNaturalSL2 in even characteristic
fingolfin Mar 31, 2026
b9b8c64
use RECOG.RecogNaturalSL2 in even char
Mar 31, 2026
b54d1b3
Add changes in RECOG.RecogNaturalSL2 see PR #434
Apr 1, 2026
7905fd7
Adjust tests
fingolfin Apr 2, 2026
3a32b3d
oops
fingolfin Apr 2, 2026
433e49e
return of RECOG.ConRecogNaturalSL2 in odd char should be pretty again
Apr 2, 2026
e56197b
Add SL24 recognition and some minor edits
Apr 8, 2026
10cfede
Add more SL(2,4) tests and some minor changes
Apr 8, 2026
1ea0c93
Remove redundant tests
Apr 28, 2026
060db70
Apply suggestion from @fingolfin
Till-Eisen Apr 28, 2026
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1 change: 0 additions & 1 deletion .github/workflows/CI.yml
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Expand Up @@ -29,7 +29,6 @@ jobs:
- '4.15'
- '4.14'
- '4.13'
- '4.12'

steps:
- uses: actions/checkout@v6
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2 changes: 1 addition & 1 deletion PackageInfo.g
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Expand Up @@ -266,7 +266,7 @@ PackageDoc := rec(
),

Dependencies := rec(
GAP := ">=4.12",
GAP := ">=4.13",
NeededOtherPackages := [
["AtlasRep", ">= 1.4.0"],
["FactInt", ">= 1.5.2"],
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222 changes: 0 additions & 222 deletions contrib/frank/sl2/NatSL2q.g
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9 changes: 2 additions & 7 deletions gap/projective/classicalnatural.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -926,13 +926,8 @@ function(ri)

# This is (P)SL2, lets set up the recognition:
Info(InfoRecog,2,"ClassicalNatural: this is PSL_2!");
if IsEvenInt(q) then
std := RECOG.RecogniseSL2NaturalEvenChar(gm,f,false);
ri!.comment := "PSL2Even";
else
std := RECOG.RecogniseSL2NaturalOddCharUsingBSGS(gm,f);
ri!.comment := "PSL2Odd";
fi;
std := RECOG.ConRecogNaturalSL2(gm,f);
ri!.comment := "PSL2";
Setslptonice(ri,SLPOfElms(std.all));
ri!.nicebas := std.bas;
ri!.nicebasi := std.basi;
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6 changes: 1 addition & 5 deletions gap/projective/sl.gi
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Expand Up @@ -72,11 +72,7 @@ RECOG.FindStdGens_SL := function(sld)
Info(InfoRecog,2,
"Recognising this SL2 constructively in 2 dimensions...");
sl2genss := GeneratorsWithMemory(sl2genss);
if IsEvenInt(q) then
resl2 := RECOG.RecogniseSL2NaturalEvenChar(Group(sl2genss),f,false);
else
resl2 := RECOG.RecogniseSL2NaturalOddCharUsingBSGS(Group(sl2genss),f);
fi;
resl2 := RECOG.ConRecogNaturalSL2(Group(sl2genss),f);
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Till-Eisen marked this conversation as resolved.
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slpsl2std := SLPOfElms(resl2.all);
bas := resl2.bas * bas;
# We need the actual transvections:
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