CHANGELOG

CHANGELOG.md

@@ -265,10 +265,11 @@ polynomial.
 ## 0.5.1.0 - 2024-05-XX
 
 * An error in an internal function resulted in an error in `groebnerBasis`. It
-has been fixed. However, while it generally works fine, I still encountered a 
-problem with `groebnerBasis` for an example, and I have not been able to find 
-the error yet. The problem with this example is that the Gröbner basis is 
-abnormally large, and then I modified the algorithm so that it throws an error 
-now when a limit is exceeded. This is just a temporary "fix".
+has been fixed. 
+
+* A limit on the number of elements of a Gröbner basis has been set in the 
+algorithm performed by `groebnerBasis`. When this limit is attained, an error 
+is thrown. The reason of this limit is that I encountered an example of a 
+large Gröbner basis and the algorithm took a quite long time.
 
 * There was an error in `esPolynomial`.

scripts/groebner-bug.hs

@@ -0,0 +1,14 @@
+import Math.Algebra.Hspray
+
+x1 = qlone 1
+x2 = qlone 2
+x3 = qlone 3
+x4 = qlone 4
+sprays = [
+    esPolynomial 4 1
+  , x1^*^x2 ^+^ x1^*^x3 ^+^ x1^*^x4 ^+^ x2^*^x3
+  , esPolynomial 4 3
+  , esPolynomial 4 4 ]
+generators = zipWith (^-^) sprays [qlone (4 + i) | i <- [1 .. 4]]
+
+gbasis = groebnerBasis generators False

src/Math/Algebra/Hspray.hs

@@ -2116,7 +2116,7 @@ groebner00 sprays = go 0 j0 combins0 spraysMap
           -> HashMap Int (Spray a, Term a) -> [Spray a]
     go !i !j !combins !gpolysMap
       | j == 100 = error 
-        "groebnerBasis: it seems that something is going wrong; please fill an issue."
+          "groebnerBasis: stopped because reached the limit; please fill an issue."
       | i == length combins = map fst (HM.elems gpolysMap)
       | otherwise           = go i' j' combins' gpolysMap'
         where