Simplify div of monomial and variable

src/nl_to_polynomial.jl

@@ -94,21 +94,27 @@ function _to_polynomial!(
         return a^b
     elseif _is_operator(expr, :/) && length(operands) == 2
         a, b = _to_polynomial!.(Ref(d), T, operands)
-        return a / b
-        # TODO(odow): see PR#113
-        # divisor, remainder = Base.divrem(a, b)
-        # if iszero(remainder)
-        #     return divisor
-        # else
-        #     return a / b
-        # end
+        return _checked_div(a, b)
     elseif _is_variable(expr)
         return _to_polynomial!(d, T, operands[1])
     else
         throw(InvalidNLExpression("Cannot convert `$(expr)` into a polynomial"))
     end
 end
 
+_checked_div(a, b) = a / b
+
+function _checked_div(
+    a::DynamicPolynomials.Monomial,
+    b::DynamicPolynomials.Variable,
+)
+    divisor, remainder = Base.divrem(a, b)
+    if iszero(remainder)
+        return divisor
+    end
+    return a / b
+end
+
 function _to_polynomial(expr, ::Type{T}) where {T}
     d = Dict{MOI.VariableIndex,VarType}()
     poly = _to_polynomial!(d, T, expr)

test/qcqp.jl

@@ -215,6 +215,38 @@ function test_scalar_nonlinear_function(x, y, T)
     return
 end
 
+function test_scalar_nonlinear_function_div_rem_zero(x, y, T)
+    inner = Model{T}()
+    model = PolyJuMP.JuMP.GenericModel{T}() do
+        return PolyJuMP.QCQP.Optimizer{T}(MOI.Utilities.MockOptimizer(inner))
+    end
+    PolyJuMP.@variable(model, x)
+    PolyJuMP.@objective(model, Min, x^3 / x)
+    PolyJuMP.optimize!(model)
+    @test MOI.get(inner, MOI.NumberOfVariables()) == 1
+    @test isempty(MOI.get(inner, MOI.ListOfConstraintTypesPresent()))
+    @test PolyJuMP.objective_function(model) isa PolyJuMP.GenericNonlinearExpr
+    F = MOI.get(inner, MOI.ObjectiveFunctionType())
+    @test F <: MOI.ScalarQuadraticFunction{T}
+    return
+end
+
+test_scalar_nonlinear_function_div_rem_one(x, y, ::Type{Int}) = nothing
+
+function test_scalar_nonlinear_function_div_rem_one(x, y, T)
+    inner = Model{T}()
+    model = PolyJuMP.JuMP.GenericModel{T}() do
+        return PolyJuMP.QCQP.Optimizer{T}(MOI.Utilities.MockOptimizer(inner))
+    end
+    PolyJuMP.@variable(model, x)
+    PolyJuMP.@objective(model, Min, x^3 / 2)
+    PolyJuMP.optimize!(model)
+    @test MOI.get(inner, MOI.NumberOfVariables()) == 2
+    F, S = MOI.ScalarQuadraticFunction{T}, MOI.EqualTo{T}
+    @test (F, S) in MOI.get(inner, MOI.ListOfConstraintTypesPresent())
+    return
+end
+
 function test_variable_primal(x, y, T)
     inner = Model{T}()
     optimizer = MOI.Utilities.MockOptimizer(inner)