fix objective size when setting quadratic term (#25)

* fix resize

* add test

ilpy/impl/solvers/Objective.cpp

@@ -37,6 +37,11 @@ Objective::getCoefficients() const {
 void
 Objective::setQuadraticCoefficient(unsigned int varNum1, unsigned int varNum2, double coef) {
 
+	if (varNum1 >= size())
+		resize(varNum1 + 1);
+	if (varNum2 >= size())
+		resize(varNum2 + 1);
+
 	if (coef == 0) {
 
 		_quadraticCoefs.erase(std::make_pair(varNum1, varNum2));

tests/test_objective.py

@@ -0,0 +1,16 @@
+import ilpy
+
+
+def test_resize() -> None:
+    obj = ilpy.Objective()
+    assert len(obj) == 0
+
+    obj.set_coefficient(0, 2)  # linear term (2x)
+    assert len(obj) == 1
+
+    obj.set_quadratic_coefficient(1, 1, 3)  # quadratic term (3y^2)
+    assert len(obj) == 2
+
+    obj2 = ilpy.Objective()
+    obj2.set_quadratic_coefficient(0, 0, 1)  # quadratic term (x^2)
+    assert len(obj2) == 1