fix a bug in Coefficients

resolves #5334
gap-system · Jan 19, 2023 · 1f90b51 · 1f90b51
1 parent 0adf6d1
commit 1f90b51
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Showing 2 changed files with 11 additions and 3 deletions.
diff --git a/lib/vspcrow.gi b/lib/vspcrow.gi
@@ -336,6 +336,7 @@ COEFFS_SEMI_ECH_BASIS:=function( B, v )
  local vectors, # basis vectors of `B'
  heads, # heads info of `B'
  len, # length of `v'
+ F, # allowed coefficients
  coeff, # coefficients list, result
  i, # loop over `v'
  pos; # heads position
@@ -351,6 +352,7 @@ COEFFS_SEMI_ECH_BASIS:=function( B, v )
  if len <> Length( heads ) then
  return fail;
  fi;
+ F:= LeftActingDomain( UnderlyingLeftModule( B ) );
 
  # Preset the coefficients list with zeroes.
  coeff:= ListWithIdenticalEntries( Length( vectors ), Zero( v[1] ) );
@@ -360,11 +362,11 @@ COEFFS_SEMI_ECH_BASIS:=function( B, v )
  i:= PositionNonZero( v );
  while i <= len do
  pos:= heads[i];
- if pos <> 0 then
+ if pos = 0 or not v[i] in F then
+ return fail;
+ else
  coeff[ pos ]:= v[i];
  AddRowVector( v, vectors[ pos ], - v[i] );
- else
- return fail;
  fi;
  i:= PositionNonZero( v );
  od;

diff --git a/tst/testinstall/vspcrow.tst b/tst/testinstall/vspcrow.tst
@@ -91,6 +91,12 @@ gap> BaseDomain( b[1] );
 GF(2^2)
 gap> b[1] = vecs[1];
 true
+gap> v:= GF(2)^1;;
+gap> b:= Basis( v, [ [ Z(2) ] ] );;
+gap> Coefficients( b, [ Z(4) ] );
+fail
+gap> SiftedVector( b, [ Z(4) ] );
+fail
 
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