def METHOD_NAME(self):
    """ Retrieve the objective value.
    Returns:
        float:
            Objective value.
    Raises:
        ValueError:
            If optimal objective value could not be retrieved.
    """
    try:
        obj_val = pyo.value(self.ef.EF_Obj)
    except Exception as e:
        raise ValueError(f"Could not extract EF objective value with error: {str(e)}")
    return obj_val