132 lines
3.5 KiB
ReStructuredText
132 lines
3.5 KiB
ReStructuredText
:orphan:
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#####################
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Train a model (basic)
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#####################
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**Audience**: Users who need to train a model without coding their own training loops.
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----
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***********
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Add imports
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***********
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Add the relevant imports at the top of the file
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.. code:: python
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import os
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import torch
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from torch import nn
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import torch.nn.functional as F
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from torchvision import transforms
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from torchvision.datasets import MNIST
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from torch.utils.data import DataLoader
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import lightning as L
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----
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*****************************
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Define the PyTorch nn.Modules
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*****************************
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.. code:: python
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class Encoder(nn.Module):
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def __init__(self):
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super().__init__()
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self.l1 = nn.Sequential(nn.Linear(28 * 28, 64), nn.ReLU(), nn.Linear(64, 3))
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def forward(self, x):
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return self.l1(x)
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class Decoder(nn.Module):
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def __init__(self):
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super().__init__()
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self.l1 = nn.Sequential(nn.Linear(3, 64), nn.ReLU(), nn.Linear(64, 28 * 28))
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def forward(self, x):
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return self.l1(x)
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----
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************************
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Define a LightningModule
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************************
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The LightningModule is the full **recipe** that defines how your nn.Modules interact.
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- The **training_step** defines how the *nn.Modules* interact together.
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- In the **configure_optimizers** define the optimizer(s) for your models.
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.. code:: python
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class LitAutoEncoder(L.LightningModule):
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def __init__(self, encoder, decoder):
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super().__init__()
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self.encoder = encoder
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self.decoder = decoder
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def training_step(self, batch, batch_idx):
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# training_step defines the train loop.
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x, _ = batch
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x = x.view(x.size(0), -1)
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z = self.encoder(x)
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x_hat = self.decoder(z)
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loss = F.mse_loss(x_hat, x)
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return loss
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def configure_optimizers(self):
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optimizer = torch.optim.Adam(self.parameters(), lr=1e-3)
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return optimizer
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----
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***************************
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Define the training dataset
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***************************
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Define a PyTorch :class:`~torch.utils.data.DataLoader` which contains your training dataset.
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.. code-block:: python
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dataset = MNIST(os.getcwd(), download=True, transform=transforms.ToTensor())
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train_loader = DataLoader(dataset)
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----
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***************
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Train the model
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***************
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To train the model use the Lightning :doc:`Trainer <../common/trainer>` which handles all the engineering and abstracts away all the complexity needed for scale.
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.. code-block:: python
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# model
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autoencoder = LitAutoEncoder(Encoder(), Decoder())
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# train model
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trainer = L.Trainer()
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trainer.fit(model=autoencoder, train_dataloaders=train_loader)
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----
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***************************
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Eliminate the training loop
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***************************
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Under the hood, the Lightning Trainer runs the following training loop on your behalf
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.. code:: python
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autoencoder = LitAutoEncoder(Encoder(), Decoder())
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optimizer = autoencoder.configure_optimizers()
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for batch_idx, batch in enumerate(train_loader):
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loss = autoencoder.training_step(batch, batch_idx)
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loss.backward()
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optimizer.step()
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optimizer.zero_grad()
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The power of Lightning comes when the training loop gets complicated as you add validation/test splits, schedulers, distributed training and all the latest SOTA techniques.
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With Lightning, you can add mix all these techniques together without needing to rewrite a new loop every time.
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