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Training Loop

The lightning training loop handles everything except the actual computations of your model. To decide what will happen in your training loop, define the training_step function.

Below are all the things lightning automates for you in the training loop.


Accumulated gradients

Accumulated gradients runs K small batches of size N before doing a backwards pass. The effect is a large effective batch size of size KxN.

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# DEFAULT (ie: no accumulated grads)
trainer = Trainer(accumulate_grad_batches=1)

Force training for min or max epochs

It can be useful to force training for a minimum number of epochs or limit to a max number

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# DEFAULT
trainer = Trainer(min_nb_epochs=1, max_nb_epochs=1000)

Force disable early stop

Use this to turn off early stopping and run training to the max_epoch

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# DEFAULT
trainer = Trainer(enable_early_stop=True)

Gradient Clipping

Gradient clipping may be enabled to avoid exploding gradients. Specifically, this will clip the gradient norm computed over all model parameters together.

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# DEFAULT (ie: don't clip)
trainer = Trainer(gradient_clip=0)

# clip gradients with norm above 0.5
trainer = Trainer(gradient_clip=0.5)

Inspect gradient norms

Looking at grad norms can help you figure out where training might be going wrong.

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# DEFAULT (-1 doesn't track norms)
trainer = Trainer(track_grad_norm=-1)

# track the LP norm (P=2 here)
trainer = Trainer(track_grad_norm=2)

Set how much of the training set to check

If you don't want to check 100% of the training set (for debugging or if it's huge), set this flag.

train_percent_check will be overwritten by overfit_pct if overfit_pct > 0

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# DEFAULT
trainer = Trainer(train_percent_check=1.0)

# check 10% only
trainer = Trainer(train_percent_check=0.1)