Add effective_variables

Author: blegat

src/polynomial.jl

@@ -1,6 +1,6 @@
 export polynomial, polynomial!, polynomialtype, terms, nterms, coefficients, monomials
 export coefficienttype, monomialtype
-export mindegree, maxdegree, extdegree
+export mindegree, maxdegree, extdegree, effective_variables
 export leadingterm, leadingcoefficient, leadingmonomial
 export removeleadingterm, removemonomials, monic
 
@@ -258,6 +258,11 @@ function extdegree(p::Union{AbstractPolynomialLike, AbstractVector{<:AbstractTer
     (mindegree(p, args...), maxdegree(p, args...))
 end
 
+function effective_variables(p::AbstractPolynomialLike, args...)
+    VT = variable_union_type(p)
+    return VT[v for v in variables(p) if !iszero(maxdegree(p, v))]
+end
+
 """
     leadingterm(p::AbstractPolynomialLike)
 

src/variable.jl

@@ -1,4 +1,4 @@
-export name, name_base_indices, similarvariable, @similarvariable
+export name, name_base_indices, similarvariable, @similarvariable, variable_union_type
 
 Base.copy(x::AbstractVariable) = x
 

test/monomial.jl

@@ -51,4 +51,19 @@ const MP = MultivariatePolynomials
     @test adjoint(x) == x
     @test transpose(x^2) == x^2
     @test adjoint(x^2) == x^2
+
+    @testset "Effective variables" begin
+        T = variable_union_type(x)
+        @test x isa T
+        @test y[2] isa T
+        @test T[x, y[2]] == @inferred effective_variables(x * y[2])
+        @test T[x, y[2]] == @inferred effective_variables(y[2] * x)
+        @test T[x] == @inferred effective_variables(x * y[2]^0)
+        @test T[x] == @inferred effective_variables(y[2]^0 * x)
+        @test T[y[2]] == @inferred effective_variables(x^0 * y[2])
+        @test T[y[2]] == @inferred effective_variables(y[2] * x^0)
+        @test T[x, y[2]] == @inferred effective_variables(y[3]^0 * x * y[2])
+        @test T[x, y[2]] == @inferred effective_variables(y[2] * y[3]^0 * x)
+        @test T[x, y[2]] == @inferred effective_variables(y[2] * x * y[3]^0)
+    end
 end

test/polynomial.jl

@@ -154,4 +154,16 @@ const MP = MultivariatePolynomials
         @test variables(v)[1] == x
         @test variables(v)[2] == y
     end
+
+    @testset "Effective variables" begin
+        Mod.@polyvar x y z
+        T = variable_union_type(x)
+        @test x isa T
+        @test y isa T
+        @test z isa T
+        @test T[x] == @inferred effective_variables(x + y - y)
+        @test T[x, y] == @inferred effective_variables(z + x + y - z)
+        @test T[y, z] == @inferred effective_variables(z + 0 * x + y)
+        @test T[z] == @inferred effective_variables(z + 0 * x + y^0)
+    end
 end

test/term.jl

@@ -48,4 +48,17 @@
 
     @test_throws InexactError push!([1], 2x)
     @test_throws ErrorException push!([x^2], 2x)
+
+
+    @testset "Effective variables" begin
+        T = variable_union_type(x)
+        @test x isa T
+        @test y isa T
+        @test T[x, y] == @inferred effective_variables(x * y)
+        @test T[x, y] == @inferred effective_variables(y * x)
+        @test T[x] == @inferred effective_variables(x * y^0)
+        @test T[x] == @inferred effective_variables(y^0 * x)
+        @test T[y] == @inferred effective_variables(x^0 * y)
+        @test T[y] == @inferred effective_variables(y * x^0)
+    end
 end

test/variable.jl

@@ -49,6 +49,11 @@ import MultivariatePolynomials: AbstractVariable, similarvariable, @similarvaria
                 end
             end
         end
+
+        @testset "Effective variables" begin
+            @test [x] == @inferred effective_variables(x)
+            @test [y] == @inferred effective_variables(y)
+        end
     end
     @testset "Create similar variable" begin
         Mod.@polyvar x y