116 lines
3.8 KiB
ReStructuredText
Executable File
116 lines
3.8 KiB
ReStructuredText
Executable File
.. testsetup:: *
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from pytorch_lightning.trainer.trainer import Trainer
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from pytorch_lightning.core.lightning import LightningModule
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Learning Rate Finder
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--------------------
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For training deep neural networks, selecting a good learning rate is essential
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for both better performance and faster convergence. Even optimizers such as
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`Adam` that are self-adjusting the learning rate can benefit from more optimal
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choices.
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To reduce the amount of guesswork concerning choosing a good initial learning
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rate, a `learning rate finder` can be used. As described in this `paper <https://arxiv.org/abs/1506.01186>`_
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a learning rate finder does a small run where the learning rate is increased
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after each processed batch and the corresponding loss is logged. The result of
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this is a `lr` vs. `loss` plot that can be used as guidance for choosing a optimal
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initial lr.
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Warnings:
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- For the moment, this feature only works with models having a single optimizer.
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- LR support for DDP is not implemented yet, it is comming soon.
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Using Lightning's built-in LR finder
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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In the most basic use case, this feature can be enabled during trainer construction
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with ``Trainer(auto_lr_find=True)``. When ``.fit(model)`` is called, the LR finder
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will automatically be run before any training is done. The ``lr`` that is found
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and used will be written to the console and logged together with all other
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hyperparameters of the model.
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.. testcode::
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# default: no automatic learning rate finder
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trainer = Trainer(auto_lr_find=False)
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This flag sets your learning rate which can be accessed via ``self.lr`` or ``self.learning_rate``.
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.. testcode::
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class LitModel(LightningModule):
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def __init__(self, learning_rate):
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self.learning_rate = learning_rate
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def configure_optimizers(self):
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return Adam(self.parameters(), lr=(self.lr or self.learning_rate))
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# finds learning rate automatically
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# sets hparams.lr or hparams.learning_rate to that learning rate
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trainer = Trainer(auto_lr_find=True)
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To use an arbitrary value set it in the parameter.
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.. testcode::
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# to set to your own hparams.my_value
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trainer = Trainer(auto_lr_find='my_value')
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Under the hood, when you call fit, this is what happens.
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1. Run learning rate finder.
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2. Run actual fit.
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.. code-block:: python
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# when you call .fit() this happens
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# 1. find learning rate
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# 2. actually run fit
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trainer.fit(model)
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If you want to inspect the results of the learning rate finder before doing any
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actual training or just play around with the parameters of the algorithm, this
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can be done by invoking the ``lr_find`` method of the trainer. A typical example
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of this would look like
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.. code-block:: python
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model = MyModelClass(hparams)
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trainer = Trainer()
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# Run learning rate finder
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lr_finder = trainer.lr_find(model)
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# Results can be found in
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lr_finder.results
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# Plot with
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fig = lr_finder.plot(suggest=True)
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fig.show()
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# Pick point based on plot, or get suggestion
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new_lr = lr_finder.suggestion()
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# update hparams of the model
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model.hparams.lr = new_lr
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# Fit model
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trainer.fit(model)
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The figure produced by ``lr_finder.plot()`` should look something like the figure
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below. It is recommended to not pick the learning rate that achives the lowest
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loss, but instead something in the middle of the sharpest downward slope (red point).
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This is the point returned py ``lr_finder.suggestion()``.
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.. figure:: /_images/trainer/lr_finder.png
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The parameters of the algorithm can be seen below.
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.. autoclass:: pytorch_lightning.trainer.lr_finder.TrainerLRFinderMixin
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:members: lr_find
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:noindex:
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:exclude-members: _run_lr_finder_internally, save_checkpoint, restore
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