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lib: improve error handling for Image, Images, ...
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..., PreImage, and PreImages.

If one of these functions figures out that the second argument is not an
element or subset of the Range or the Source, it now tells the user.
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@ssiccha
ssiccha committed May 17, 2019
1 parent f30c1e4 commit 7fa0e7e
Showing 1 changed file with 70 additions and 30 deletions.
100 changes: 70 additions & 30 deletions lib/mapping.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -165,17 +165,22 @@ InstallGlobalFunction( Image, function ( arg )
map := arg[1];
elm := arg[2];

if FamSourceEqFamElm( FamilyObj( map ), FamilyObj( elm ) ) then
if not IsMapping( map ) then
ErrorNoReturn( "<map> must be a mapping" );
fi;

if not IsMapping( map ) then
Error( "<map> must be a mapping" );
elif elm in Source( map ) then
return ImageElm( map, elm );
# image of a single element <elm> under the mapping <map>
if FamSourceEqFamElm( FamilyObj( map ), FamilyObj( elm ) ) then
if not elm in Source( map ) then
ErrorNoReturn( "<elm> must be an element of Source(<map>)" );
fi;
return ImageElm( map, elm );

# image of a set or list of elments <elm> under the mapping <map>
elif CollFamSourceEqFamElms( FamilyObj( map ), FamilyObj(elm) )
and IsSubset( Source( map ), elm ) then
elif CollFamSourceEqFamElms( FamilyObj( map ), FamilyObj(elm) ) then
if not IsSubset( Source( map ), elm ) then
ErrorNoReturn( "<coll> must be a subset of Source(<map>)" );
fi;

if IsDomain( elm ) or IsSSortedList( elm ) then
if HasSource(map) and IsIdenticalObj(Source(map),elm) then
Expand All @@ -185,16 +190,23 @@ InstallGlobalFunction( Image, function ( arg )
fi;
elif IsHomogeneousList( elm ) then
return ImagesSet( map, Set( elm ) );
else
ErrorNoReturn( "<coll> must be a domain, a set, ",
"or a homogeneous list" );
fi;

# image of the empty list
elif IsList( elm ) and IsEmpty( elm ) then

return [];

else
ErrorNoReturn( "could not match the family of <elm> or <coll> to ",
"the family of Source(<map>)" );
fi;
fi;
Error( "usage: Image(<map>), Image(<map>,<elm>), Image(<map>,<coll>)" );
ErrorNoReturn( "usage: Image(<map>), Image(<map>,<elm>), ",
"Image(<map>,<coll>)" );
end );


Expand All @@ -220,33 +232,43 @@ InstallGlobalFunction( Images, function ( arg )
elm := arg[2];

if not IsGeneralMapping( map ) then
Error( "<map> must be a general mapping" );
ErrorNoReturn( "<map> must be a general mapping" );
fi;

# image of a single element <elm> under the mapping <map>
if FamSourceEqFamElm( FamilyObj( map ), FamilyObj( elm ) )
and elm in Source( map ) then

if FamSourceEqFamElm( FamilyObj( map ), FamilyObj( elm ) ) then
if not elm in Source( map ) then
ErrorNoReturn( "<elm> must be an element of Source(<map>)" );
fi;
return ImagesElm( map, elm );

# image of a set or list of elments <elm> under the mapping <map>
elif CollFamSourceEqFamElms( FamilyObj( map ), FamilyObj(elm) )
and IsSubset( Source( map ), elm ) then
elif CollFamSourceEqFamElms( FamilyObj( map ), FamilyObj(elm) ) then
if not IsSubset( Source( map ), elm ) then
ErrorNoReturn( "<coll> must be a subset of Source(<map>)" );
fi;

if IsDomain( elm ) or IsSSortedList( elm ) then
return ImagesSet( map, elm );
elif IsHomogeneousList( elm ) then
return ImagesSet( map, Set( elm ) );
else
ErrorNoReturn( "<coll> must be a domain, a set, ",
"or a homogeneous list" );
fi;

# image of the empty list
elif IsList( elm ) and IsEmpty( elm ) then

return [];

else
ErrorNoReturn( "could not match the family of <elm> or <coll> to ",
"the family of Source(<map>)" );
fi;
fi;
Error("usage: Images(<map>), Images(<map>,<elm>), Images(<map>,<coll>)");
ErrorNoReturn( "usage: Images(<map>), Images(<map>,<elm>), ",
"Images(<map>,<coll>)" );
end );


Expand Down Expand Up @@ -275,30 +297,39 @@ InstallGlobalFunction( PreImage, function ( arg )
if FamRangeEqFamElm( FamilyObj( map ), FamilyObj( img ) ) then
if not ( IsGeneralMapping( map ) and IsInjective( map )
and IsSurjective( map ) ) then
Error( "<map> must be an inj. and surj. mapping" );
elif img in Range( map ) then
return PreImageElm( map, img );
ErrorNoReturn( "<map> must be an inj. and surj. mapping" );
elif not img in Range( map ) then
ErrorNoReturn( "<elm> must be an element of Range(<map>)" );
fi;
return PreImageElm( map, img );

# preimage of a set or list of elments <img> under <map>
elif CollFamRangeEqFamElms( FamilyObj( map ), FamilyObj( img ) )
and IsSubset( Range( map ), img ) then
elif CollFamRangeEqFamElms( FamilyObj( map ), FamilyObj( img ) ) then
if not IsSubset( Range( map ), img ) then
ErrorNoReturn( "<coll> must be a subset of Range(<map>)" );
fi;

if IsDomain( img ) or IsSSortedList( img ) then
return PreImagesSet( map, img );
elif IsHomogeneousList( img ) then
return PreImagesSet( map, Set( img ) );
else
ErrorNoReturn( "<coll> must be a domain, a set, ",
"or a homogeneous list" );
fi;

# preimage of the empty list
elif IsList( img ) and IsEmpty( img ) then

return [];

else
ErrorNoReturn( "could not match the family of <elm> or <coll> to ",
"the family of Source(<map>)" );
fi;
fi;
Error( "usage: PreImage(<map>), PreImage(<map>,<img>), ",
"PreImage(<map>,<coll>)" );
ErrorNoReturn( "usage: PreImage(<map>), PreImage(<map>,<img>), ",
"PreImage(<map>,<coll>)" );
end );


Expand All @@ -324,34 +355,43 @@ InstallGlobalFunction( PreImages, function ( arg )
img := arg[2];

if not IsGeneralMapping( map ) then
Error( "<map> must be a general mapping" );
ErrorNoReturn( "<map> must be a general mapping" );
fi;

# preimage of a single element <img> under <map>
if FamRangeEqFamElm( FamilyObj( map ), FamilyObj( img ) )
and img in Range( map ) then

if FamRangeEqFamElm( FamilyObj( map ), FamilyObj( img ) ) then
if not img in Range( map ) then
ErrorNoReturn( "<elm> must be an element of Range(<map>)" );
fi;
return PreImagesElm( map, img );

# preimage of a set or list of elements <img> under <map>
elif CollFamRangeEqFamElms( FamilyObj( map ), FamilyObj( img ) )
and IsSubset( Range( map ), img ) then
elif CollFamRangeEqFamElms( FamilyObj( map ), FamilyObj( img ) ) then
if not IsSubset( Range( map ), img ) then
ErrorNoReturn( "<coll> must be a subset of Range(<map>)" );
fi;

if IsDomain( img ) or IsSSortedList( img ) then
return PreImagesSet( map, img );
elif IsHomogeneousList( img ) then
return PreImagesSet( map, Set( img ) );
else
ErrorNoReturn( "<coll> must be a domain, a set, ",
"or a homogeneous list" );
fi;

# preimage of the empty list
elif IsList( img ) and IsEmpty( img ) then

return [];

else
ErrorNoReturn( "could not match the family of <elm> or <coll> to ",
"the family of Source(<map>)" );
fi;
fi;
Error( "usage: PreImages(<map>), PreImages(<map>,<img>), ",
"PreImages(<map>,<coll>)" );
ErrorNoReturn( "usage: PreImages(<map>), PreImages(<map>,<img>), ",
"PreImages(<map>,<coll>)" );
end );


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