metric constraint (#90)

* penalty change

* metric modification

* catboost init

flaml/automl.py

@@ -922,6 +922,7 @@ class AutoML:
         # set up learner search space
         for estimator_name in estimator_list:
             estimator_class = self._state.learner_classes[estimator_name]
+            estimator_class.init()
             self._search_states[estimator_name] = SearchState(
                 learner_class=estimator_class,
                 data_size=self._state.data_size, task=self._state.task,

flaml/model.py

@@ -163,6 +163,11 @@ class BaseEstimator:
         '''[optional method] relative cost compared to lightgbm'''
         return 1.0
 
+    @classmethod
+    def init(cls):
+        '''[optional method] initialize the class'''
+        pass
+
 
 class SKLearnEstimator(BaseEstimator):
 
@@ -632,6 +637,11 @@ class CatBoostEstimator(BaseEstimator):
     def cost_relative2lgbm(cls):
         return 15
 
+    @classmethod
+    def init(cls):
+        CatBoostEstimator._time_per_iter = None
+        CatBoostEstimator._train_size = 0
+
     def __init__(
         self, task='binary:logistic', n_jobs=1,
         n_estimators=8192, learning_rate=0.1, early_stopping_rounds=4, **params

flaml/searcher/blendsearch.py

@@ -27,6 +27,8 @@ class BlendSearch(Searcher):
     '''
 
     cost_attr = "time_total_s"  # cost attribute in result
+    lagrange = '_lagrange'      # suffix for lagrange-modified metric
+    penalty = 1e+10             # penalty term for constraints
 
     def __init__(self,
                  metric: Optional[str] = None,
@@ -106,6 +108,11 @@ class BlendSearch(Searcher):
         self._metric, self._mode = metric, mode
         init_config = low_cost_partial_config or {}
         self._points_to_evaluate = points_to_evaluate or []
+        self._config_constraints = config_constraints
+        self._metric_constraints = metric_constraints
+        if self._metric_constraints:
+            # metric modified by lagrange
+            metric += self.lagrange
         if global_search_alg is not None:
             self._gs = global_search_alg
         elif getattr(self, '__name__', None) != 'CFO':
@@ -115,8 +122,6 @@ class BlendSearch(Searcher):
         self._ls = LocalSearch(
             init_config, metric, mode, cat_hp_cost, space,
             prune_attr, min_resource, max_resource, reduction_factor, seed)
-        self._config_constraints = config_constraints
-        self._metric_constraints = metric_constraints
         self._init_search()
 
     def set_search_properties(self,
@@ -131,6 +136,11 @@ class BlendSearch(Searcher):
         else:
             if metric:
                 self._metric = metric
+                if self._metric_constraints:
+                    # metric modified by lagrange
+                    metric += self.lagrange
+                    # TODO: don't change metric for global search methods that
+                    # can handle constraints already
             if mode:
                 self._mode = mode
             self._ls.set_search_properties(metric, mode, config)
@@ -156,6 +166,13 @@ class BlendSearch(Searcher):
         self._gs_admissible_max = self._ls_bound_max.copy()
         self._result = {}  # config_signature: tuple -> result: Dict
         self._deadline = np.inf
+        if self._metric_constraints:
+            self._metric_constraint_satisfied = False
+            self._metric_constraint_penalty = [
+                self.penalty for _ in self._metric_constraints]
+        else:
+            self._metric_constraint_satisfied = True
+            self._metric_constraint_penalty = None
 
     def save(self, checkpoint_path: str):
         save_object = self
@@ -182,6 +199,8 @@ class BlendSearch(Searcher):
         self._ls = state._ls
         self._config_constraints = state._config_constraints
         self._metric_constraints = state._metric_constraints
+        self._metric_constraint_satisfied = state._metric_constraint_satisfied
+        self._metric_constraint_penalty = state._metric_constraint_penalty
 
     def restore_from_dir(self, checkpoint_dir: str):
         super.restore_from_dir(checkpoint_dir)
@@ -190,10 +209,11 @@ class BlendSearch(Searcher):
                           error: bool = False):
         ''' search thread updater and cleaner
         '''
+        metric_constraint_satisfied = True
         if result and not error and self._metric_constraints:
-            # accout for metric constraints if any
+            # account for metric constraints if any
             objective = result[self._metric]
-            for constraint in self._metric_constraints:
+            for i, constraint in enumerate(self._metric_constraints):
                 metric_constraint, sign, threshold = constraint
                 value = result.get(metric_constraint)
                 if value:
@@ -202,8 +222,16 @@ class BlendSearch(Searcher):
                     violation = (value - threshold) * sign_op
                     if violation > 0:
                         # add penalty term to the metric
-                        objective += 1e+10 * violation * self._ls.metric_op
-            result[self._metric] = objective
+                        objective += self._metric_constraint_penalty[
+                            i] * violation * self._ls.metric_op
+                        metric_constraint_satisfied = False
+                        if self._metric_constraint_penalty[i] < self.penalty:
+                            self._metric_constraint_penalty[i] += violation
+            result[self._metric + self.lagrange] = objective
+            if metric_constraint_satisfied and not self._metric_constraint_satisfied:
+                # found a feasible point
+                self._metric_constraint_penalty = [1 for _ in self._metric_constraints]
+            self._metric_constraint_satisfied |= metric_constraint_satisfied
         thread_id = self._trial_proposed_by.get(trial_id)
         if thread_id in self._search_thread_pool:
             self._search_thread_pool[thread_id].on_trial_complete(
@@ -219,10 +247,13 @@ class BlendSearch(Searcher):
             else:  # add to result cache
                 self._result[self._ls.config_signature(config)] = result
                 # update target metric if improved
-                objective = result[self._metric]
+                objective = result[
+                    self._metric + self.lagrange] if self._metric_constraints \
+                    else result[self._metric]
                 if (objective - self._metric_target) * self._ls.metric_op < 0:
                     self._metric_target = objective
-                if not thread_id and self._create_condition(result):
+                if not thread_id and metric_constraint_satisfied \
+                        and self._create_condition(result):
                     # thread creator
                     self._search_thread_pool[self._thread_count] = SearchThread(
                         self._ls.mode,
@@ -233,6 +264,9 @@ class BlendSearch(Searcher):
                     self._thread_count += 1
                     self._update_admissible_region(
                         config, self._ls_bound_min, self._ls_bound_max)
+                elif thread_id and not self._metric_constraint_satisfied:
+                    # no point has been found to satisfy metric constraint
+                    self._expand_admissible_region()
                 # reset admissible region to ls bounding box
                 self._gs_admissible_min.update(self._ls_bound_min)
                 self._gs_admissible_max.update(self._ls_bound_max)
@@ -306,6 +340,8 @@ class BlendSearch(Searcher):
         thread_id = self._trial_proposed_by[trial_id]
         if thread_id not in self._search_thread_pool:
             return
+        if result and self._metric_constraints:
+            result[self._metric + self.lagrange] = result[self._metric]
         self._search_thread_pool[thread_id].on_trial_result(trial_id, result)
 
     def suggest(self, trial_id: str) -> Optional[Dict]: