add new function check_same_variable which checks non-constant polynomials equality of variable; close #217

Author: jverzani

Project.toml

@@ -2,7 +2,7 @@ name = "Polynomials"
 uuid = "f27b6e38-b328-58d1-80ce-0feddd5e7a45"
 license = "MIT"
 author = "JuliaMath"
-version = "1.0.4"
+version = "1.0.5"
 
 [deps]
 Intervals = "d8418881-c3e1-53bb-8760-2df7ec849ed5"

src/common.jl

@@ -253,6 +253,14 @@ variable(::Type{P}, var::SymbolLike = :x) where {P <: AbstractPolynomial} = P([0
 variable(p::AbstractPolynomial, var::SymbolLike = p.var) = variable(typeof(p), var)
 variable(var::SymbolLike = :x) = variable(Polynomial{Int})
 
+"""
+    check_same_variable(p::AbstractPolynomial, q::AbstractPolynomial)
+
+Check if either `p` or `q` is constant or if `p` and `q` share the same variable
+"""
+check_same_variable(p::AbstractPolynomial, q::AbstractPolynomial) =
+    (Polynomials.isconstant(p) || Polynomials.isconstant(q)) || p.var ==  q.var
+
 #=
 Linear Algebra =#
 """
@@ -318,6 +326,17 @@ has a nonzero coefficient. The degree of the zero polynomial is defined to be -1
 """
 degree(p::AbstractPolynomial) = iszero(p) ? -1 : length(p) - 1
 
+
+"""
+    isconstant(::AbstractPolynomial)
+
+Is the polynomial  `p` a constant.
+"""
+isconstant(p::AbstractPolynomial) = degree(p) <= 0
+
+
+
+
 hasnan(p::AbstractPolynomial) = any(isnan.(coeffs(p)))
 
 """
@@ -535,9 +554,7 @@ function Base.isapprox(p1::AbstractPolynomial{T},
     rtol::Real = (Base.rtoldefault(T, S, 0)),
     atol::Real = 0,) where {T,S}
     p1, p2 = promote(p1, p2)
-    if p1.var != p2.var
-        error("p1 and p2 must have same var")
-    end
+    check_same_variable(p1, p2)  || error("p1 and p2 must have same var")
     p1t = truncate(p1; rtol = rtol, atol = atol)
     p2t = truncate(p2; rtol = rtol, atol = atol)
     if length(p1t) ≠ length(p2t)

src/polynomials/ImmutablePolynomial.jl

@@ -154,7 +154,7 @@ function Base.isapprox(p1::ImmutablePolynomial{N,T},
                        p2::ImmutablePolynomial{M,S};
                        rtol::Real = (Base.rtoldefault(T, S, 0)),
                        atol::Real = 0,) where {N,T,M,S}
-    p1.var == p2.var || error("p1 and p2 must have same var")
+    check_same_variable(p1, p2) || error("p1 and p2 must have same var")
     NN = max(N,M)
     for i in 1:NN-1
         isapprox(p1[i],p2[i], rtol=rtol, atol=atol) || return false

src/polynomials/standard-basis.jl

@@ -83,7 +83,8 @@ end
 
 
 function Base.divrem(num::P, den::Q) where {P <: StandardBasisPolynomial, Q <: StandardBasisPolynomial}
-    num.var != den.var && error("Polynomials must have same variable")
+
+    check_same_variable(num, den) || error("Polynomials must have same variable")
     var = num.var
 
 

test/StandardBasis.jl

@@ -229,6 +229,12 @@ end
 
         @test P([0.5]) + 2 == P([2.5])
         @test 2 - P([0.5]) == P([1.5])
+
+        # check isapprox ignores variable mismatch when constants are involved, issue #217
+        @test Polynomial(1, :x) ≈ Polynomial(1, :y)
+        @test (variable(Polynomial, :x) ≈ variable(Polynomial, :x))
+        @test_throws ErrorException variable(Polynomial, :x) ≈ variable(Polynomial, :y)
+
     end
 end