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Use GAP library function PositionNonZero #23

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Merged
margollo merged 1 commit into from
Sep 13, 2025
Merged

Use GAP library function PositionNonZero #23

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15 changes: 4 additions & 11 deletions gap/grpalg/collect.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -5,13 +5,6 @@
##
## functions to work with tables (in the sense of ModIsom) which correspond to quotients of the augmentation ideal I of a group algebra of a finite p-group over a field of characteristic p modulo a power of I. In particular, to generate the table for this quotient

# Input: A list
# Output: The nonzero positions of the list
BindGlobal("PosNonzero", function(list)
return PositionsProperty(list, x -> not IsZero(x));
end);


# Input: Linear combination of words. A word is a list of pairs of natural numbers. We think e.g. g1^2*g3 = [[1,2],[3,1]]
# Output: Same linear combination (in the math sense) where each word
# appears at most once
Expand Down Expand Up @@ -198,7 +191,7 @@ local w, sw, pos, p;

sw := 0;
w := [ ];
pos := PosNonzero(exp);
pos := PositionNonZero(exp);

for p in pos do
sw := sw + 1;
Expand Down Expand Up @@ -443,7 +436,7 @@ local F, p, exp, pos1, i, j, pows, pos, combs, v, c, w, s, m, tup, coefprod, exp
# Check if weight of p-th power exceeds level
if p*T.pre.weights[i] <= lvl then
pows := StructuralCopy(T.pre.jen.pows[pos1]);
pos := PosNonzero(pows);
pos := PositionNonZero(pows);
pows := pows{pos};
combs := Combinations([1..Length(pos)]);
Remove(combs, 1);
Expand Down Expand Up @@ -523,7 +516,7 @@ local F, p, exp, pos1, i, j, pows, pos, combs, v, c, w, s, m, tup, coefprod, exp
pows := StructuralCopy(T.pre.jen.coms[poscom][2]);
pows[pos1] := 1;
pows[pos2] := 1;
pos := PosNonzero(pows);
pos := PositionNonZero(pows);
pows := pows{pos};
combs := Combinations([1..Length(pos)]);
v := [ ];
Expand Down Expand Up @@ -591,7 +584,7 @@ end);
# Input: Table and maximal weight we want. Typically output from PreSet
# Output: None. T.powwords, T.commwords, T.dim, T.wgs are set
BindGlobal("WordFillTable", function(T, lvl)
local F, p, s1, l, i, pos1, expw1, w1, sortweights1, sortexpw1, f1, posf1, s2, post2, expw2, w2, sortweights2, sortexpw2, f2, posf2, dep, mm, vec, posvec, fac1, posnonzero, v;
local F, p, s1, l, i, pos1, expw1, w1, sortweights1, sortexpw1, f1, posf1, s2, post2, expw2, w2, sortweights2, sortexpw2, f2, posf2, dep, mm, vec, posvec, fac1, v;

F := T.fld;
p := Characteristic(F);
Expand Down
2 changes: 1 addition & 1 deletion gap/grpalg/tabletoalgebraandback.gi
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Expand Up @@ -24,7 +24,7 @@ local k, maxweight, i, lim, sup, coeffs, v0, res, exps, nonzeroexps, sum, S, ini
## for each element g1^e1...gm^em we convert g1^e1...gm^em to an expression in the Jennings basis using the formulas known for this
for i in [1..Size(sup)] do
exps := ExponentsOfPcElement(T.pre.jen.pcgs, sup[i]){[1..lim]};
nonzeroexps := PosNonzero(exps);
nonzeroexps := PositionNonZero(exps);
sum := ShallowCopy(v0);
# run over all supsets of non-zero exponents. Each gives a summand
for S in Combinations( nonzeroexps ) do
Expand Down
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