Added MIP bilinear test. Also, we now allow constraints to have param…

…s which are not in model.

symfit/core/models.py

@@ -198,8 +198,7 @@ def as_constraint(cls, constraint, model, constraint_type=None, **init_kwargs):
         if set(instance.params) <= set(model.params):
             instance.params = model.params
         else:
-            raise ModelError('The parameters of ``constraint`` have to be a '
-                             'subset of those of ``model``.')
+            model.params = sorted(set(model.params) | set(instance.params), key=lambda x: x.name)
 
         return instance
 

tests/test_mip.py

@@ -13,7 +13,7 @@ def test_parameter_array_bounds():
 
 
 def test_bilinear():
-    # Create variables
+    # Solve the bilinear example with MIP and compare to Fit.
     x, y, z = parameters('x, y, z', min=0)
 
     objective = 1.0 * x
@@ -25,8 +25,10 @@ def test_bilinear():
 
     mip = MIP(- objective, constraints=constraints)
     mip_result = mip.execute()
-    print(mip_result)
-
     fit = Fit(- objective, constraints=constraints)
     fit_result = fit.execute()
-    print(fit_result)
+
+    assert mip_result[x] == pytest.approx(fit_result.value(x), abs=1e-6)
+    assert mip_result[y] == pytest.approx(fit_result.value(y), abs=1e-6)
+    assert mip_result[z] == pytest.approx(fit_result.value(z), abs=1e-6)
+    assert mip_result.objective_value == pytest.approx(fit_result.objective_value, abs=1e-6)