fixed yonedaExtension for multigraded rings

mikestillman · Oct 16, 2024 · 1c121d0 · 1c121d0
1 parent 2caeddf
commit 1c121d0
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Showing 2 changed files with 5 additions and 3 deletions.
diff --git a/M2/Macaulay2/packages/Complexes/ChainComplex.m2 b/M2/Macaulay2/packages/Complexes/ChainComplex.m2
@@ -1155,7 +1155,7 @@ yonedaExtension Matrix := Complex => f -> (
     g := homomorphism E.cache.yonedaExtension f; -- g: FM_d --> N
     -- if g has a non-zero degree, we must twist the target to preserve homogeneity
     gdegree := degree g;
-    g = map(N ** (ring g)^gdegree, source g, g);
+    g = map(N ** (ring g)^{gdegree}, source g, g);
     if d <= 0 then error "Yoneda extension only defined for Ext^d module for d at least 1";
     h := dd^FM_d || g;
     P := coker h; -- FM_d --> FM_(d-1) ++ N --> P --> 0

diff --git a/M2/Macaulay2/packages/Complexes/ChainComplexTests.m2 b/M2/Macaulay2/packages/Complexes/ChainComplexTests.m2
@@ -2009,10 +2009,12 @@ TEST ///
   restart
   needsPackage "Complexes"
 *-
-
   S = ZZ/101[a..d, Degrees=>{2:{1,0},2:{0,1}}]
   B = ideal(a,b) * ideal(c,d)
-  Ext^1(B, S)
+  E = Ext^1(B, S)
+  C = yonedaExtension map(E, , matrix random cover E)
+  assert(C_0 == module B)
+  assert(C_2 == module S)
   F = random({1,2}, S)
   f = map(S^1, S^{-degree F}, {{F}})
   assert isHomogeneous f