100 lines
3.0 KiB
ReStructuredText
100 lines
3.0 KiB
ReStructuredText
Optimization
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===============
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Learning rate scheduling
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-------------------------------------
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Every optimizer you use can be paired with any `LearningRateScheduler <https://pytorch.org/docs/stable/optim.html#how-to-adjust-learning-rate>`_.
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.. code-block:: python
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# no LR scheduler
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def configure_optimizers(self):
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return Adam(...)
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# Adam + LR scheduler
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def configure_optimizers(self):
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return [Adam(...)], [ReduceLROnPlateau()]
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# Two optimziers each with a scheduler
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def configure_optimizers(self):
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return [Adam(...), SGD(...)], [ReduceLROnPlateau(), LambdaLR()]
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Use multiple optimizers (like GANs)
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-------------------------------------
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To use multiple optimizers return > 1 optimizers from :meth:`pytorch_lightning.core.LightningModule.configure_optimizers`
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.. code-block:: python
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# one optimizer
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def configure_optimizers(self):
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return Adam(...)
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# two optimizers, no schedulers
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def configure_optimizers(self):
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return Adam(...), SGD(...)
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# Two optimizers, one scheduler for adam only
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def configure_optimizers(self):
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return [Adam(...), SGD(...)], [ReduceLROnPlateau()]
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Lightning will call each optimizer sequentially:
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.. code-block:: python
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for epoch in epochs:
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for batch in data:
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for opt in optimizers:
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train_step(opt)
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opt.step()
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for scheduler in scheduler:
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scheduler.step()
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Step optimizers at arbitrary intervals
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----------------------------------------
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To do more interesting things with your optimizers such as learning rate warm-up or odd scheduling,
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override the :meth:`optimizer_step` function.
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For example, here step optimizer A every 2 batches and optimizer B every 4 batches
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.. code-block:: python
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def optimizer_step(self, current_epoch, batch_nb, optimizer, optimizer_i, second_order_closure=None):
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optimizer.step()
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optimizer.zero_grad()
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# Alternating schedule for optimizer steps (ie: GANs)
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def optimizer_step(self, current_epoch, batch_nb, optimizer, optimizer_i, second_order_closure=None):
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# update generator opt every 2 steps
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if optimizer_i == 0:
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if batch_nb % 2 == 0 :
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optimizer.step()
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optimizer.zero_grad()
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# update discriminator opt every 4 steps
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if optimizer_i == 1:
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if batch_nb % 4 == 0 :
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optimizer.step()
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optimizer.zero_grad()
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# ...
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# add as many optimizers as you want
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Here we add a learning-rate warm up
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.. code-block:: python
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# learning rate warm-up
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def optimizer_step(self, current_epoch, batch_nb, optimizer, optimizer_i, second_order_closure=None):
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# warm up lr
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if self.trainer.global_step < 500:
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lr_scale = min(1., float(self.trainer.global_step + 1) / 500.)
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for pg in optimizer.param_groups:
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pg['lr'] = lr_scale * self.hparams.learning_rate
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# update params
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optimizer.step()
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optimizer.zero_grad()
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