Fix IsMonomialMatrix for compressed matrices

Note that for MatrixObj implementations which are *not* lists, doing `for row in M do` may not work anymore (unless we decide to officially define that `Iterator(matobj)` shall return a row iterator).
gap-system · Dec 29, 2018 · 6780172 · 6780172
1 parent cf47710
commit 6780172
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Showing 2 changed files with 5 additions and 1 deletion.
diff --git a/lib/matrix.gi b/lib/matrix.gi
@@ -2574,7 +2574,7 @@ InstallMethod( IsMonomialMatrix,
     if Length( M ) <> len  then
         return false;
     fi;
-    found:= BlistList( M, [] );
+    found:= ListWithIdenticalEntries( len, false );
     for row  in M  do
         j := PositionNonZero( row );
         if len < j or found[j]  then

diff --git a/tst/testbugfix/2018-12-28-IsMonomialMatrix.tst b/tst/testbugfix/2018-12-28-IsMonomialMatrix.tst
@@ -0,0 +1,4 @@
+gap> Number(SL(2,2), IsMonomialMatrix);
+2
+gap> Number(SL(2,3), IsMonomialMatrix);
+4
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,4 @@
		gap> Number(SL(2,2), IsMonomialMatrix);
		2
		gap> Number(SL(2,3), IsMonomialMatrix);
		4