adjusts converted input if Oscar input generators contain zero elements

Author: ederc

src/algorithms/groebner-bases.jl

@@ -147,7 +147,8 @@ function _core_groebner_basis(
         error("At the moment we only supports finite fields.")
     end
 
-    lens, cfs, exps = _convert_to_msolve(F)
+    # nr_gens might change if F contains zero polynomials
+    lens, cfs, exps, nr_gens = _convert_to_msolve(F)
 
     gb_ld  = Ref(Cint(0))
     gb_len = Ref(Ptr{Cint}(0))

src/interfaces/nemo.jl

@@ -21,6 +21,8 @@ function _convert_to_msolve(
     if field_char > 2^31 || degree(base_ring(R)) != 1
         error("At the moment we only support prime fields up to prime characteristic < 2^31.")
     end
+
+    lens = Int32[]
     # get coefficients
     if field_char == 0
         cfs = BigInt[]
@@ -29,15 +31,21 @@ function _convert_to_msolve(
     end
     if field_char == 0
         for i in 1:nr_gens
-            for cf in coefficients(F[i])
-                push!(cfs, BigInt(numerator(cf)))
-                push!(cfs, BigInt(denominator(cf)))
+            if F[i] != R(0)
+                for cf in coefficients(F[i])
+                    push!(cfs, BigInt(numerator(cf)))
+                    push!(cfs, BigInt(denominator(cf)))
+                end
+                push!(lens, length(F[i]))
             end
         end
     else
         for i in 1:nr_gens
-            for cf in coefficients(F[i])
-                push!(cfs, Int32(lift(Nemo.ZZ, cf)))
+            if F[i] != R(0)
+                for cf in coefficients(F[i])
+                    push!(cfs, Int32(lift(Nemo.ZZ, cf)))
+                end
+                push!(lens, length(F[i]))
             end
         end
     end
@@ -50,7 +58,7 @@ function _convert_to_msolve(
         end
     end
 
-    return lens, cfs, exps
+    return lens, cfs, exps, length(lens)
 end
 
 @doc Markdown.doc"""