Merge pull request #3292 from LukasKuehne/matroid_realization_spaces

Fixed two bugs in the matroid realization code

experimental/MatroidRealizationSpaces/src/realization_space.jl

@@ -394,7 +394,7 @@ function realization_space(
     RS = reduce_realization_space(RS)
   end
 
-  if q != nothing
+  if q != nothing && RS.ambient_ring isa MPolyRing
     I = RS.defining_ideal
     R = RS.ambient_ring
     eqs = Vector{RingElem}()
@@ -820,11 +820,14 @@ function reduce_realization_space(
       normal_Sgens = Vector{RingElem}()
     else
       Sgens_new = phi.(Sgens)
-      normal_Sgens = gens_2_prime_divisors([normal_form(g, Inew) for g in Sgens_new])
+      normal_Sgens = [normal_form(g, Inew) for g in Sgens_new]
+      if !(ambR(0) in normal_Sgens)
+        normal_Sgens = gens_2_prime_divisors(Sgens_new)
+      end
     end
   end
 
-  if isone(Inew)
+  if isone(Inew) || ambR(0) in normal_Sgens
     MRS_new = MatroidRealizationSpace(Inew, normal_Sgens, ambR, nothing, MRS.char, MRS.q, MRS.ground_ring)
     set_attribute!(MRS_new, :is_realizable, :false)
     return MRS_new

experimental/MatroidRealizationSpaces/test/runtests.jl

@@ -12,6 +12,23 @@
     x1 = gens(R1)
     x2 = gens(R2)
     x3 = gens(R3)
+
+    @testset "is_realizable" begin
+        @test is_realizable(M1) == true
+        @test is_realizable(M2) == true
+        @test is_realizable(M3) == false
+        @test is_realizable(M4) == true
+
+        @test is_realizable(M1, char = 2) == true
+        @test is_realizable(M1, char = 3) == false
+        @test is_realizable(M1, q = 2) == true
+        @test is_realizable(M1, q = 3) == false
+
+        @test is_realizable(M2, char = 2) == true
+        @test is_realizable(M2, char = 3) == true
+        @test is_realizable(M2, q = 2) == false
+        @test is_realizable(M2, q = 7) == true
+    end
 
     @testset "realization_space_matrix" begin