remove comment and add new ambiguous example (#1665)

thofma · Oct 29, 2024 · 2b1fd06 · 2b1fd06
1 parent 5601795
commit 2b1fd06
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Showing 3 changed files with 12 additions and 6 deletions.
diff --git a/src/QuadForm/Quad/GenusRep.jl b/src/QuadForm/Quad/GenusRep.jl
@@ -2135,7 +2135,7 @@ end
 
 function _lattice_to_binary_quadratic_form(L::QuadLat)
   M = absolute_basis_matrix(L) # This corresponds to a basis of L
-  @assert nrows(M) == 2 && ncols(M) == 2
+  @assert nrows(M) == 2
   G = gram_matrix(ambient_space(L), M)
   GG = change_base_ring(FlintQQ, G)
   d = denominator(GG)
@@ -2284,10 +2284,6 @@ function automorphism_group_generators(g::QuadBin{ZZRingElem})
       f = matrix(ZZ, 2, 2, [a, b, n, -a])
       push!(gens, t* f * inv(t))
     end
-    # Stevell can make sense of this:
-#     if is_ambiguous && !(a==0 ||(a != 0 && c ==0 && b % (2*a) == 0))
-#       error("missing case")
-#    end
     for T in gens
       @assert _action(g, T) == g
     end

diff --git a/test/QuadForm/Quad/GenusRep.jl b/test/QuadForm/Quad/GenusRep.jl
@@ -1107,6 +1107,12 @@ end
   @test rank(L2) != degree(L2)
   Ns2 = @inferred genus_representatives(L2, use_auto = false)
   @test length(Ns2) == length(Ns)
+
+  # Binary case
+  B = matrix(FlintQQ, 2, 23 ,[1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]);
+  G = matrix(FlintQQ, 23, 23 ,[-4, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, 0, 0, -1//2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, -1//2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, -1//2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, 0, 0, -1//2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, -1//2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, -1//2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, 1, -1, 3, 1//2, -1//2, 3//2, -3//2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1, 3, -3, -1//2, 3//2, -3//2, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 3, -3, 10, 3//2, -3//2, 5, -5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, -3, 10, -10, -3//2, 5, -5, 17, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1//2, -1//2, 3//2, -3//2, -1//2, 1, -1, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1//2, 3//2, -3//2, 5, 1, -1, 3, -3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3//2, -3//2, 5, -5, -1, 3, -3, 10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -3//2, 5, -5, 17, 3, -3, 10, -10]);
+  L = integer_lattice(B, gram = G);
+  @test length(representatives(genus(L))) == 1
 end
 
 @testset "More ZZGenus representatives" begin

diff --git a/test/QuadForm/QuadBin.jl b/test/QuadForm/QuadBin.jl
@@ -216,7 +216,11 @@
 
     g = binary_quadratic_form(-4, 3, 0)
     gens = automorphism_group_generators(g)
-    @test gens == [ZZ[-1 0;0 -1], ZZ[-4 3; -5 4]]
+    @test gens == [ZZ[-1 0; 0 -1], ZZ[-4 3; -5 4]]
+
+    g = binary_quadratic_form(-4, 16, 0)
+    gens = automorphism_group_generators(g)
+    @test gens == [ZZ[-1 0; 0 -1], ZZ[-1 4; 0 1]]
 
     g = binary_quadratic_form(1, 2, 0)
     gens = automorphism_group_generators(g)