Merge pull request #35 from ederc/zero-input

Zero input handling

Author: ederc

src/algorithms/groebner-bases.jl

@@ -131,6 +131,9 @@ function _core_groebner_basis(
 
     F = I.gens
     R = first(F).parent
+    if F == [R(0)]
+        return F
+    end
     nr_vars     = nvars(R)
     nr_gens     = length(F)
     field_char  = Int(characteristic(R))

src/algorithms/normal-forms.jl

@@ -121,10 +121,18 @@ function _core_normal_form(
 
     #= first get a degree reverse lexicographical Gröbner basis for I =#
     if !haskey(I.gb, 0)
-        groebner_basis(I, eliminate = 0, la_option = 44, info_level = info_level)
+        if field_char > 2^17
+            groebner_basis(I, eliminate = 0, la_option = 44, info_level = info_level)
+        else
+            groebner_basis(I, eliminate = 0, la_option = 2, info_level = info_level)
+        end
     end
     G = I.gb[0]
 
+    if G == [R(0)]
+        return F
+    end
+
     tbr_nr_gens = length(F)
     bs_nr_gens  = length(G)
     is_gb       = 1

test/algorithms/groebner-bases.jl

@@ -25,6 +25,10 @@
     L = eliminate(I,2)
     @test L == H
     @test I.gb[2] == H
+
+    I = Ideal([R(0)])
+    G = groebner_basis(I)
+    @test G == [R(0)]
 end
 
 @testset "Algorithms -> Sig Gröbner bases" begin

test/algorithms/normal-forms.jl

@@ -13,4 +13,6 @@
     I = Ideal([y*x+17-y, x+13*y])
     F = [x+13*y, x*y+16]
     @test normal_form(F, I) == [0, y + 65520]
+    I = Ideal([R(0)])
+    @test normal_form(F, I) == F
 end