From 68939f2e4da8befd3833eaac46fba0ecabaa564e Mon Sep 17 00:00:00 2001
From: Oscar Dowson <odow@users.noreply.github.com>
Date: Mon, 4 Mar 2024 22:54:07 +1300
Subject: [PATCH] Fix final_touch if no higher-order polynomials are present
 (#109)

* Fix final_touch if no higher-order polynomials are present

* Add test
---
 src/QCQP/MOI_wrapper.jl | 38 ++++++++++++++++++++------------------
 test/qcqp.jl            | 13 +++++++++++++
 2 files changed, 33 insertions(+), 18 deletions(-)

diff --git a/src/QCQP/MOI_wrapper.jl b/src/QCQP/MOI_wrapper.jl
index 9e6d25d..cb1e79f 100644
--- a/src/QCQP/MOI_wrapper.jl
+++ b/src/QCQP/MOI_wrapper.jl
@@ -318,25 +318,27 @@ function MOI.Utilities.final_touch(model::Optimizer{T}, _) where {T}
             end
         end
     end
-    div = decompose(monos)
-    for mono in sort(collect(keys(div)))
-        if haskey(vars, mono)
-            continue
+    if !isnothing(monos)
+        div = decompose(monos)
+        for mono in sort(collect(keys(div)))
+            if haskey(vars, mono)
+                continue
+            end
+            a = div[mono]
+            monomial_variable_index(model, vars, div, a)
+            b = MP.div_multiple(mono, a)
+            monomial_variable_index(model, vars, div, b)
+        end
+        if !isnothing(model.objective)
+            func, index_to_var = _subs!(model.objective, index_to_var)
+            obj = _quad_convert(func.polynomial, vars, div)
+            MOI.set(model.model, MOI.ObjectiveFunction{typeof(obj)}(), obj)
+        end
+        for S in keys(model.constraints)
+            F = PolyJuMP.ScalarPolynomialFunction{T,model.constraints[S][1]}
+            cis = MOI.get(model, MOI.ListOfConstraintIndices{F,S}())
+            _add_constraints(model, cis, index_to_var, vars, div)
         end
-        a = div[mono]
-        monomial_variable_index(model, vars, div, a)
-        b = MP.div_multiple(mono, a)
-        monomial_variable_index(model, vars, div, b)
-    end
-    if !isnothing(model.objective)
-        func, index_to_var = _subs!(model.objective, index_to_var)
-        obj = _quad_convert(func.polynomial, vars, div)
-        MOI.set(model.model, MOI.ObjectiveFunction{typeof(obj)}(), obj)
-    end
-    for S in keys(model.constraints)
-        F = PolyJuMP.ScalarPolynomialFunction{T,model.constraints[S][1]}
-        cis = MOI.get(model, MOI.ListOfConstraintIndices{F,S}())
-        _add_constraints(model, cis, index_to_var, vars, div)
     end
     return
 end
diff --git a/test/qcqp.jl b/test/qcqp.jl
index 427111c..45af152 100644
--- a/test/qcqp.jl
+++ b/test/qcqp.jl
@@ -144,6 +144,19 @@ function test_objective_and_constraint(x, y, T)
           o * a3 * b3 + o * a6
 end
 
+function test_no_monomials(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, 0 <= x[1:2] <= 1)
+    PolyJuMP.@constraint(model, x[1] * x[2] == 0.5)
+    PolyJuMP.@objective(model, Min, sum(x))
+    PolyJuMP.optimize!(model)
+    @test MOI.get(inner, MOI.NumberOfVariables()) == 2
+    return
+end
+
 function runtests(x, y)
     for name in names(@__MODULE__; all = true)
         if startswith("$name", "test_")