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Update of sparse.gi file #166

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Merged
grahamknockillaree merged 2 commits into from
Oct 14, 2026
Merged

Update of sparse.gi file #166

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16f7939
Update sparse.gi
giuliao27 Oct 14, 2026
ffdd9ce
Merge branch 'gap-packages:master' into master
giuliao27 Oct 14, 2026
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21 changes: 8 additions & 13 deletions lib/Sparse/sparse.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -369,37 +369,32 @@ end);
#####################################################################
InstallGlobalFunction(NullspaceSparseMatDestructive,
function(B)
local NS, heads, free, vec, revcol, pos, i,v,w, x,y,z,h,s;
local NS, heads, free, i, v, x, y, z, h, s;

NS:=[];

if not IsBound(B!.heads) then
SparseSemiEchelon(B);
fi;

heads:=Filtered([1..B!.cols],x->IsBound(B!.heads[x]));
heads:=Filtered([1..B!.cols],x->B!.heads[x]<>0);

free:=Difference([1..B!.cols],heads);
revcol:=Reversed([1..B!.cols]);

for x in free do
v:=[];
Add(v,[x,1]);
v:=ListWithIdenticalEntries(B!.cols,0);
v[x]:=1;

for y in revcol do
if y in heads then
for y in Reversed(heads) do
h:=B!.mat[B!.heads[y]];

s:=0;
for z in h do
pos:=PositionProperty(v,a->a[1]=z[1]);
if IsInt(pos) then s:=s+z[2]*v[pos][2]; fi;
s:=s+z[2]*v[z[1]];
od;
if not s=0 then Add(v,[y,-s]); fi;
fi;
v[y]:=-s;
od;

Add(NS,v);
Add(NS, Filtered(List([1..B!.cols],i->[i,v[i]]), p->not IsZero(p[2])));

od;
return NS;
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