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AddToIgs improvements 2: Don't call GcdPara when we can predict it won't make any changes #236

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Merged
fingolfin merged 2 commits into from
Oct 16, 2026
Merged

AddToIgs improvements 2: Don't call GcdPara when we can predict it won't make any changes #236

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8934692
More mini-optimisations for AddToIgs code
stertooy Oct 12, 2026
91e5d59
Merge branch 'master' into igs-improv-2
fingolfin Oct 16, 2026
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31 changes: 20 additions & 11 deletions gap/basic/pcppara.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ end );
##
InstallGlobalFunction( AddToIgsParallel,
function( pcs, gens, ppcs, pgens )
local coll, rels, n, inf, todo, tododo, ind, indd, g, gg, d, h, hh, k,
local coll, rels, n, inf, todo, tododo, ind, indd, g, gg, d, h, hh, a, b, q, k,
c, i, r, sub, keep, val, j, f, nrmd, pairs;

if Length( gens ) = 0 then return [pcs, ppcs]; fi;
Expand Down Expand Up @@ -172,16 +172,25 @@ function( pcs, gens, ppcs, pgens )
g := g^0;
gg := gg^0;
else
pairs := GcdPcpPara(g, h, gg, hh);
h := pairs[1];
g := pairs[2];
hh := pairs[3];
gg := pairs[4];
if h <> ind[d] then
nrmd := NormedPcpElementPara( h, hh );
ind[d] := nrmd[1];
indd[d] := nrmd[2];
AddSet(f, d);
a := LeadingExponent(g);
b := LeadingExponent(h);
if a > 0 and b > 0 and a mod b = 0 then
# GcdPcpPara would leave h and hh unchanged.
q := a/b;
g := g * h^-q;
gg := gg * hh^-q;
else
pairs := GcdPcpPara(g, h, gg, hh);
h := pairs[1];
g := pairs[2];
hh := pairs[3];
gg := pairs[4];
if h <> ind[d] then
nrmd := NormedPcpElementPara( h, hh );
ind[d] := nrmd[1];
indd[d] := nrmd[2];
AddSet(f, d);
fi;
fi;
fi;
d := Depth(g);
Expand Down
21 changes: 14 additions & 7 deletions gap/basic/pcppcps.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -136,7 +136,7 @@ end );
#F AddToIgs( <igs>, <gens> )
##
InstallGlobalFunction(AddToIgs, function(igs, gens)
local coll, rels, n, inf, c, ind, g, d, todo, val, j, f, h, k, pair, t;
local coll, rels, n, inf, c, ind, g, d, todo, val, j, f, h, a, b, k, pair, t;

if Length(gens) = 0 then return igs; fi;

Expand Down Expand Up @@ -176,12 +176,19 @@ InstallGlobalFunction(AddToIgs, function(igs, gens)
if g = h then
g := g^0;
else
pair := GcdPcp(g, h);
h := pair[1];
g := pair[2];
if h <> ind[d] then
ind[d] := NormedPcpElement( h );
AddSet(f, d);
a := LeadingExponent(g);
b := LeadingExponent(h);
if a > 0 and b > 0 and a mod b = 0 then
# GcdPcp would leave h unchanged.
g := g * h^(-a/b);
else
pair := GcdPcp(g, h);
h := pair[1];
g := pair[2];
if h <> ind[d] then
ind[d] := NormedPcpElement( h );
AddSet(f, d);
fi;
fi;
fi;
d := Depth(g);
Expand Down
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