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Fix AsPartialPerm method for transformations #1036

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Jan 3, 2017
Merged

Fix AsPartialPerm method for transformations #1036

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21 changes: 3 additions & 18 deletions doc/ref/pperm.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -1068,7 +1068,6 @@ gap> AsPartialPerm(f, [ 1, 2, 3 ] );
set of positive integer"/>
<Meth Name="AsPartialPerm" Arg="f, n" Label="for a transformation and a
positive integer"/>
<Meth Name="AsPartialPerm" Arg="f" Label="for a transformation"/>
<Returns>A partial permutation or <K>fail</K>.</Returns>
<Description>
A transformation <A>f</A> defines a partial permutation when it is
Expand All @@ -1095,33 +1094,19 @@ gap> AsPartialPerm(f, [ 1, 2, 3 ] );
integer and this set satisfies the
conditions given above.
</Item>
<Mark>for a transformation</Mark>
<Item>
Let <C>n</C> denote the degree of <A>f</A>. If
<C>n^<A>f</A>=n</C> and <A>f</A> is injective on those <C>i</C> such
that <C>i^<A>f</A>&lt;>n</C>, then <C>AsPartialPerm</C> returns
the partial permutation obtained by restricting <A>f</A> to those
<C>i</C> such that <C>i^<A>f</A>&lt;>n</C>.
</Item>
</List>

<C>AsPartialPerm</C> returns <K>fail</K> if the arguments do not describe a
partial permutation.<P/>

The operation <Ref Oper="PartialPermOp"/> can also be used to convert
transformations into partial permutations.

<Example>
gap> f:=Transformation( [ 8, 3, 5, 9, 6, 2, 9, 7, 9 ] );;
gap> AsPartialPerm(f);
[1,8,7](2,3,5,6)
gap> AsPartialPerm(f, [1, 2, 3, 5, 8]);
[1,8,7][2,3,5,6]
gap> AsPartialPerm(f, 3);
[1,8][2,3,5]
gap> AsPartialPerm(f, [ 2 .. 4 ] );
[2,3,5][4,9]
gap> f:=Transformation( [ 2, 10, 2, 4, 4, 7, 6, 9, 10, 1 ] );;
gap> AsPartialPerm(f);
fail</Example>
[2,3,5][4,9]</Example>
</Description>
</ManSection>
</Section>
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33 changes: 5 additions & 28 deletions lib/pperm.gi
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Expand Up @@ -229,14 +229,12 @@ InstallMethod(AsPartialPerm, "for a transformation and list",
[IsTransformation, IsList],
function(f, list)

if not IsSSortedList(list) or not ForAll(list, IsPosInt)
or not ForAll(list, i-> i<=DegreeOfTransformation(f)) then
Error("usage: the second argument must be a set of positive integers ",
"not greater than the degree of the first argument,");
return;
if not IsSSortedList(list) or not ForAll(list, IsPosInt) then
ErrorNoReturn("usage: the second argument must be a set of positive ",
"integers,");
elif not IsInjectiveListTrans(list, f) then
Error("usage: the first argument must be injective on the second,");
return fail;
ErrorNoReturn("usage: the first argument must be injective on the ",
"second,");
fi;
return PartialPermNC(list, OnTuples(list, f));
end);
Expand All @@ -249,27 +247,6 @@ function(f, n)
return AsPartialPerm(f, [1..n]);
end);

# c method? JDM

InstallMethod(AsPartialPerm, "for a transformation",
[IsTransformation],
function(f)
local img, n;
n:=DegreeOfTransformation(f);
if not n^f=n then
return fail;
fi;
return PartialPerm(List([1..n], function(i)
local j;
j:=i^f;
if j=n then
return 0;
else
return j;
fi;
end));
end);

# n is image of undefined points
InstallMethod(AsTransformation, "for a partial perm and positive integer",
[IsPartialPerm, IsPosInt],
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4 changes: 0 additions & 4 deletions tst/testinstall/pperm.tst
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Expand Up @@ -2286,17 +2286,13 @@ gap> AsTransformation(f);
<transformation: 6,2,5,10,4,7,8,9,10>
gap> AsTransformation(f, 12);
<transformation: 6,2,5,12,4,7,8,9,12,10,12>
gap> AsPartialPerm(last);
[1,6,7,8,9][3,5,4](2)(10)
gap> f;
[1,6,7,8,9][3,5,4](2)(10)
gap> f:=PartialPermNC([ 1, 3, 4, 5, 6, 9 ], [ 9, 10, 5, 7, 2, 8 ]);;
gap> AsTransformation(f);
<transformation: 9,11,10,5,7,2,11,11,8,11>
gap> AsTransformation(f);
<transformation: 9,11,10,5,7,2,11,11,8,11>
gap> AsPartialPerm(last)=f;
true
gap> OnTuples([1..DegreeOfPartialPerm(f)], f);
[ 9, 10, 5, 7, 2, 8 ]
gap> g:=PartialPermNC([ 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 19 ],
Expand Down