Fix degree with noncommutative variables (#150)

Author: blegat

src/monomial.jl

@@ -75,12 +75,14 @@ degree(v::AbstractVariable, var::AbstractVariable) = (v == var ? 1 : 0)
 #degree(m::AbstractMonomial, v::AbstractVariable) = _deg(v, powers(t)...)
 
 function degree(m::AbstractMonomial, v::AbstractVariable)
-    i = findfirst(isequal(v), variables(m))
-    if i === nothing || iszero(i)
-        0
-    else
-        exponents(m)[i]
+    deg = 0
+    # With Noncommutative variables, there may be several powers with the same variable
+    for (var, exp) in powers(m)
+        if var == v
+            deg += exp
+        end
     end
+    return deg
 end
 
 """

test/ncmonomial.jl

@@ -24,6 +24,13 @@
             @test collect(exponents(Y)) == [2]
         end
     end
+    @testset "Issue #148" begin
+        Mod.@ncpolyvar x y z
+        m = x * y^4 * x^2
+        @test 3 == @inferred degree(m, x)
+        @test 4 == @inferred degree(m, y)
+        @test 0 == @inferred degree(m, z)
+    end
     @testset "Issue #71 of DynamicPolynomials" begin
         Mod.@ncpolyvar x y
         @test x^0 * y == y * x^0