Add ordering for a vector of variables (#327)

* Add ordering for a vector of variables

* Add tests

Author: blegat

src/comparison.jl

@@ -328,6 +328,10 @@ function ordering end
 ordering(::Type{<:AbstractMonomial}) = Graded{LexOrder}
 ordering(::Type{P}) where {P} = ordering(monomial_type(P))
 ordering(p::AbstractPolynomialLike) = ordering(typeof(p))
+# Useful for instance to ask ordering given the list
+# of variables
+ordering(::AbstractVector{T}) where {T} = ordering(T)
+ordering(t::Tuple) = ordering(first(t))
 
 # We reverse the order of comparisons here so that the result
 # of x < y is equal to the result of Monomial(x) < Monomial(y)

test/commutative/comparison.jl

@@ -1,6 +1,10 @@
 @testset "Comparison" begin
     @testset "Graded Lex Order" begin
         Mod.@polyvar x y z
+        O = Graded{LexOrder}
+        @test ordering(x) == O
+        @test ordering(x * y) == O
+        @test ordering(variables(x * y)) == O
         @test x > y > z
         @test x^2 * y > y^3 > z
         @test y^2 >= x