fixed a bug in basis'

mahrud · Nov 22, 2024 · b137b77 · b137b77
1 parent a7adc8c
commit b137b77
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Showing 2 changed files with 15 additions and 4 deletions.
diff --git a/M2/Macaulay2/packages/Truncations.m2 b/M2/Macaulay2/packages/Truncations.m2
@@ -359,11 +359,15 @@ basis'(List, Module) := Matrix => opts -> (degs, M) -> (
     if M == 0 then return map(M, 0, 0);
     if not truncateImplemented(R := ring M) then error "cannot use basis' with this ring type";
     degs = checkOrMakeDegreeList(degs, degreeLength R);
+    B := if isFreeModule M then (
+	map(M, , basisMonomials(degs, M, "partial degrees" => opts#"partial degrees")))
     -- TODO: "mingens image" seems silly ...
-    B := map(M, , if not M.?relations
-    then basisMonomials(degs, M, "partial degrees" => opts#"partial degrees")
-    else reduce(super M, raw basis'(degs, image generators M, opts)));
-    inducedMap(M, , mingens image B))
+    else if not M.?relations then map(M, ,
+	mingens image basisMonomials(degs, cover M, "partial degrees" => opts#"partial degrees"))
+    else inducedMap(M, ,
+	mingens image map(ambient M, ,
+	    reduce(super M, raw gens image basis'(degs, image generators M))))
+    )
 
 --------------------------------------------------------------------
 ----- Tests section

diff --git a/M2/Macaulay2/packages/Truncations/basis-tests.m2 b/M2/Macaulay2/packages/Truncations/basis-tests.m2
@@ -85,3 +85,10 @@ TEST ///
   (t, B) = toSequence elapsedTiming basis(degree D, S^1);
   assert(numcols B == 11 and t < 10)
 ///
+
+TEST ///
+  needsPackage "NormalToricVarieties"
+  X = hirzebruchSurface 2
+  M = cotangentSheaf X
+  assert(HH^1(X, M) == QQ^2)
+///