[Major] simplify learning rate finder and use log-mean of default and…

… smooth suggestion (#1630)

* simplify learning rate finder

* set learning rate to logarithmic mean of smooth and default.

* move logic to util

neuralprophet/configure.py

@@ -208,7 +208,7 @@ def set_lr_finder_args(self, dataset_size, num_batches):
         Set the lr_finder_args.
         This is the range of learning rates to test.
         """
-        num_training = 150 + int(np.log10(100 + dataset_size) * 25)
+        num_training = 100 + int(np.log10(dataset_size) * 20)
         if num_batches < num_training:
             log.warning(
                 f"Learning rate finder: The number of batches ({num_batches}) is too small than the required number \
@@ -217,7 +217,7 @@ def set_lr_finder_args(self, dataset_size, num_batches):
             # num_training = num_batches
         self.lr_finder_args.update(
             {
-                "min_lr": 1e-6,
+                "min_lr": 1e-7,
                 "max_lr": 10,
                 "num_training": num_training,
                 "early_stop_threshold": None,

neuralprophet/forecaster.py

@@ -2805,13 +2805,12 @@ def _train(
                 lr_finder = tuner.lr_find(
                     model=self.model,
                     train_dataloaders=train_loader,
-                    val_dataloaders=val_loader,
+                    # val_dataloaders=val_loader, # not be used, but may lead to Lightning bug if not provided
                     **self.config_train.lr_finder_args,
                 )
                 # Estimate the optimal learning rate from the loss curve
                 assert lr_finder is not None
-                _, _, lr_suggestion = utils.smooth_loss_and_suggest(lr_finder.results)
-                self.model.learning_rate = lr_suggestion
+                _, _, self.model.learning_rate = utils.smooth_loss_and_suggest(lr_finder)
             start = time.time()
             self.trainer.fit(
                 self.model,
@@ -2832,8 +2831,7 @@ def _train(
                 )
                 assert lr_finder is not None
                 # Estimate the optimal learning rate from the loss curve
-                _, _, lr_suggestion = utils.smooth_loss_and_suggest(lr_finder.results)
-                self.model.learning_rate = lr_suggestion
+                _, _, self.model.learning_rate = utils.smooth_loss_and_suggest(lr_finder)
             start = time.time()
             self.trainer.fit(
                 self.model,

neuralprophet/utils.py

@@ -751,7 +751,7 @@ def set_log_level(log_level: str = "INFO", include_handlers: bool = False):
     set_logger_level(logging.getLogger("NP"), log_level, include_handlers)
 
 
-def smooth_loss_and_suggest(lr_finder_results, window=10):
+def smooth_loss_and_suggest(lr_finder, window=10):
     """
     Smooth loss using a Hamming filter.
 
@@ -769,10 +769,12 @@ def smooth_loss_and_suggest(lr_finder_results, window=10):
         suggested_lr: float
             Suggested learning rate based on gradient
     """
+    lr_finder_results = lr_finder.results
     lr = lr_finder_results["lr"]
     loss = lr_finder_results["loss"]
     # Derive window size from num lr searches, ensure window is divisible by 2
-    half_window = math.ceil(round(len(loss) * 0.1) / 2)
+    # half_window = math.ceil(round(len(loss) * 0.1) / 2)
+    half_window = math.ceil(window / 2)
     # Pad sequence and initialialize hamming filter
     loss = np.pad(np.array(loss), pad_width=half_window, mode="edge")
     window = np.hamming(half_window * 2)
@@ -798,7 +800,17 @@ def smooth_loss_and_suggest(lr_finder_results, window=10):
             "samples or manually set the learning rate."
         )
         raise
-    return (loss, lr, suggestion)
+    suggestion_default = lr_finder.suggestion(skip_begin=10, skip_end=3)
+    if suggestion is not None and suggestion_default is not None:
+        log_suggestion_smooth = np.log(suggestion)
+        log_suggestion_default = np.log(suggestion_default)
+        lr_suggestion = np.exp((log_suggestion_smooth + log_suggestion_default) / 2)
+    elif suggestion is None and suggestion_default is None:
+        log.error("Automatic learning rate test failed. Please set manually the learning rate.")
+        raise
+    else:
+        lr_suggestion = suggestion if suggestion is not None else suggestion_default
+    return (loss, lr, lr_suggestion)
 
 
 def _smooth_loss(loss, beta=0.9):