fixed bug where tuner would not tune lr if also tuning batch_size (#4688

)

* fixed bug where tuner would not tune lr if also tuning batch_size

* added a '+1' to computing the smoothed loss. This maintains the behavior for the smoothed loss as before the bug fix

* pep8 fix

* add changelog

Co-authored-by: chaton <thomas@grid.ai>
Co-authored-by: Carlos Mocholi <carlossmocholi@gmail.com>
Co-authored-by: Adrian Wälchli <aedu.waelchli@gmail.com>
(cherry picked from commit 523c59b)

CHANGELOG.md

@@ -23,6 +23,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed `Trainer` not resetting `lightning_optimizers` when calling `Trainer.fit()` multiple times ([#6372](https://github.com/PyTorchLightning/pytorch-lightning/pull/6372))
 
 
+- Fixed an issue where the tuner would not tune the learning rate if also tuning the batch size ([#4688](https://github.com/PyTorchLightning/pytorch-lightning/pull/4688))
+
+
 ## [1.2.2] - 2021-03-02
 
 ### Added

pytorch_lightning/tuner/lr_finder.py

@@ -412,11 +412,11 @@ def on_train_batch_end(self, trainer, pl_module, outputs, batch, batch_idx, data
             self.progress_bar.update()
 
         current_loss = trainer.train_loop.running_loss.last().item()
-        current_step = trainer.global_step + 1  # remove the +1 in 1.0
+        current_step = trainer.global_step
 
         # Avg loss (loss with momentum) + smoothing
         self.avg_loss = self.beta * self.avg_loss + (1 - self.beta) * current_loss
-        smoothed_loss = self.avg_loss / (1 - self.beta**current_step)
+        smoothed_loss = self.avg_loss / (1 - self.beta**(current_step + 1))
 
         # Check if we diverging
         if self.early_stop_threshold is not None: