Fixed setting of cost function when using to_function

src/hippopt/base/opti_solver.py

@@ -46,13 +46,6 @@ def __init__(self, message: Exception):
         )
 
 
-class ToFunctionSolveNotCalled(Exception):
-    def __init__(self):
-        super().__init__(
-            "The solve() method must be called before converting to function."
-        )
-
-
 @dataclasses.dataclass
 class OptiSolver(OptimizationSolver):
     DefaultSolverType: ClassVar[str] = "ipopt"
@@ -591,10 +584,8 @@ def get_free_parameters_names(self) -> list[str]:
     def to_function(
         self, name: str = "opti_function", options: dict = None
     ) -> cs.Function:
-        if self._output_solution is None:
-            # to_function does not seem to work without calling solve() first
-            raise ToFunctionSolveNotCalled
-
+        self._cost = self._cost if self._cost is not None else cs.MX(0)
+        self._solver.minimize(self._cost)
         variables_names = list(self._objects_dict.keys())
         # Prepend guess to the variable names
         guess_names = ["guess." + name for name in variables_names]

test/test_optimization_problem.py

@@ -312,12 +312,6 @@ def test_opti_to_function():
         ),
     )
 
-    problem.solver().set_initial_guess(initial_guess=initial_guess)
-    problem.solve()
-
-    c = 20.0 * np.random.rand(3, 1) - 10.0
-    initial_guess.parameter = c
-
     opti_function = opti_solver.to_function()
     output_dict = opti_function(**initial_guess.to_dict(prefix="guess."))
     output = MyTestVarAndPar()