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freeband: add method for OnePseudoInverse #1232

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freeband: add method for OnePseudoInverse #1232

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freeband: add method for OnePseudoInverse
iortas Oct 7, 2026
8441a8e
freeband: add method for OnePseudoInverse
iortas Oct 7, 2026
d7579ac
Merge branch 'one-pseudo' of https://github.com/iortas/Semigroups int…
iortas Oct 7, 2026
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4 changes: 4 additions & 0 deletions doc/attr.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -1278,6 +1278,10 @@ Error, the semigroup is not finite]]></Example>
<Item>
<Ref Prop="IsReesZeroMatrixSemigroupElement" BookName="ref"/>.
</Item>
<Mark>elements of a free band</Mark>
<Item>
<Ref Prop="IsFreeBandElement"/>.
</Item>
</List>

See also <Ref Oper="OneInverseOfSemigroupElement"/>.
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4 changes: 4 additions & 0 deletions gap/fp/freeband.gi
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Expand Up @@ -504,3 +504,7 @@ function(_, hashlen)
return rec(func := SEMIGROUPS.HashFunctionForFreeBandElements,
data := hashlen);
end);

InstallMethod(OnePseudoInverseOfSemigroupElement,
"for a free band element",
[IsFreeBandElement], IdFunc);
8 changes: 8 additions & 0 deletions tst/standard/fp/freeband.tst
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Expand Up @@ -316,6 +316,14 @@ Error, the generator names must be distinct
gap> FreeBand(["a", "x", "y", "x", "d"]);
Error, the generator names must be distinct

# OnePseudoInverseOfSemigroupElement
gap> S := FreeBand(5);
<free band on the generators [ x1, x2, x3, x4, x5 ]>
gap> z := S.1 * S.3 * S.2 * S.2 * S.5 * S.3;
x1x3x2x5x1x3x2x5x2x5x3
gap> OnePseudoInverseOfSemigroupElement(z);
x1x3x2x5x1x3x2x5x2x5x3

#
gap> SEMIGROUPS.StopTest();
gap> STOP_TEST("Semigroups package: standard/fp/freeband.tst");
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