write Training 101 guide

docs/guides/training_101/index.md

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+---
+icon: material/book
+---
+# Training 101
+
+This guide will walk you through training a model using Refiners. We built the `training_utils` module to provide a simple, flexible, statically type-safe interface.
+
+We will use a simple model and a toy dataset for demonstration purposes. The model will be a simple [autoencoder](https://en.wikipedia.org/wiki/Autoencoder), and the dataset will be a synthetic dataset of rectangles
+of different sizes.
+
+## Pre-requisites
+
+We recommend installing Refiners targeting a specific commit hash to avoid unexpected changes in the API. You also 
+get the benefit of having a perfectly reproducible environment.
+
+- with rye (recommended):
+```bash
+rye add refiners[training] --git=https://github.com/finegrain-ai/refiners.git --branch=<insert-latest-commit-hash>
+```
+
+- with pip:
+```bash
+ pip install "git+https://github.com/finegrain-ai/refiners.git@<insert-latest-commit-hash>#egg=refiners[training]"
+```
+
+## Model
+
+Let's start by building our autoencoder using Refiners.
+
+??? autoencoder "Expand to see the autoencoder model."
+
+    ```py
+    from refiners.fluxion import layers as fl
+
+
+     class ConvBlock(fl.Chain):
+        def __init__(self, in_channels: int, out_channels: int) -> None:
+            super().__init__(
+                fl.Conv2d(
+                    in_channels=in_channels,
+                    out_channels=out_channels,
+                    kernel_size=3,
+                    padding=1,
+                    groups=min(in_channels, out_channels)
+                ),
+                fl.LayerNorm2d(out_channels),
+                fl.SiLU(),
+                fl.Conv2d(
+                    in_channels=out_channels,
+                    out_channels=out_channels,
+                    kernel_size=1,
+                    padding=0,
+                ),
+                fl.LayerNorm2d(out_channels),
+                fl.SiLU(),
+            )
+
+
+    class ResidualBlock(fl.Sum):
+        def __init__(self, in_channels: int, out_channels: int) -> None:
+            super().__init__(
+                ConvBlock(in_channels=in_channels, out_channels=out_channels),
+                fl.Conv2d(
+                    in_channels=in_channels,
+                    out_channels=out_channels,
+                    kernel_size=3,
+                    padding=1,
+                ),
+            )
+
+
+    class Encoder(fl.Chain):
+        def __init__(self) -> None:
+            super().__init__(
+                ResidualBlock(in_channels=1, out_channels=8),
+                fl.Downsample(channels=8, scale_factor=2, register_shape=False),
+                ResidualBlock(in_channels=8, out_channels=16),
+                fl.Downsample(channels=16, scale_factor=2, register_shape=False),
+                ResidualBlock(in_channels=16, out_channels=32),
+                fl.Downsample(channels=32, scale_factor=2, register_shape=False),
+                fl.Reshape(2048),
+                fl.Linear(in_features=2048, out_features=256),
+                fl.SiLU(),
+                fl.Linear(in_features=256, out_features=256),
+            )
+
+
+    class Decoder(fl.Chain):
+        def __init__(self) -> None:
+            super().__init__(
+                fl.Linear(in_features=256, out_features=256),
+                fl.SiLU(),
+                fl.Linear(in_features=256, out_features=2048),
+                fl.Reshape(32, 8, 8),
+                ResidualBlock(in_channels=32, out_channels=32),
+                ResidualBlock(in_channels=32, out_channels=32),
+                fl.Upsample(channels=32, upsample_factor=2),
+                ResidualBlock(in_channels=32, out_channels=16),
+                ResidualBlock(in_channels=16, out_channels=16),
+                fl.Upsample(channels=16, upsample_factor=2),
+                ResidualBlock(in_channels=16, out_channels=8),
+                ResidualBlock(in_channels=8, out_channels=8),
+                fl.Upsample(channels=8, upsample_factor=2),
+                ResidualBlock(in_channels=8, out_channels=8),
+                ResidualBlock(in_channels=8, out_channels=1),
+                fl.Sigmoid(),
+            )
+
+
+    class Autoencoder(fl.Chain):
+        def __init__(self) -> None:
+            super().__init__(
+                Encoder(),
+                Decoder(),
+            )
+
+        @property
+        def encoder(self) -> Encoder:
+            return self.ensure_find(Encoder)
+
+        @property
+        def decoder(self) -> Decoder:
+            return self.ensure_find(Decoder)
+
+    ```
+
+We now have a fully functional autoencoder that takes an image with one channel of
+size 64x64 and compresses it to a vector of size 256 (x16 compression). The decoder then takes this vector and reconstructs the original image.
+
+```py
+import torch
+
+autoencoder = Autoencoder()
+
+x = torch.randn(2, 1, 64, 64) # batch of 2 images
+
+z = autoencoder.encoder(x) # [2, 256]
+
+x_reconstructed = autoencoder.decoder(z) # [2, 1, 64, 64]
+```
+
+## Dataset
+
+We will use a synthetic dataset of rectangles of different sizes. The dataset will be generated on the fly using this 
+simple function:
+
+```python
+import random
+from typing import Generator
+from PIL import Image
+
+from refiners.fluxion.utils import image_to_tensor
+
+def generate_mask(size: int, seed: int | None = None) -> Generator[torch.Tensor, None, None]:
+    """Generate a tensor of a grayscale mask of size `size` using random rectangles."""
+    if seed is None:
+        seed = random.randint(0, 2**32 - 1)
+    random.seed(seed)
+
+    while True:
+        rectangle = Image.new(
+            "L", (random.randint(1, size), random.randint(1, size)), color=255
+        )
+        mask = Image.new("L", (size, size))
+        mask.paste(
+            rectangle,
+            (
+                random.randint(0, size - rectangle.width),
+                random.randint(0, size - rectangle.height),
+            ),
+        )
+        tensor = image_to_tensor(mask)
+
+        if random.random() > 0.5:
+            tensor = 1 - tensor
+
+        yield tensor
+```
+
+To generate a mask, do:
+
+```python
+from refiners.fluxion.utils import tensor_to_image
+
+mask = next(generate_mask(64, seed=42))
+tensor_to_image(mask).save("mask.png")
+```
+
+Here are a few examples of generated images:
+![alt text](sample-0.png)
+![alt text](sample-1.png)
+![alt text](sample-2.png)
+
+## Trainer
+
+We will now create a Trainer class to handle the training loop. This class will manage the model, the optimizer, the loss function, and the dataset. It will also orchestrate the training loop and the evaluation loop.
+
+But first, we need to define the batch type that will be used to represent a batch for the forward and backward pass and the configuration associated with the trainer.
+
+### Batch
+
+Our batches are composed of a single tensor representing the images. We will define a simple `Batch` type to implement this.
+
+```python
+from dataclasses import dataclass
+
+@dataclass
+class Batch:
+    image: torch.Tensor
+```
+
+### Config
+
+We will now define the configuration for the autoencoder. It holds the configuration for the training loop, the optimizer, and the learning rate scheduler. It should inherit `refiners.training_utils.BaseConfig` and has the following mandatory attributes:
+
+  - `TrainingConfig`: The configuration for the training loop, including the duration of the training, the batch size, device, dtype, etc.
+  - `OptimizerConfig`: The configuration for the optimizer, including the learning rate, weight decay, etc.
+  - `LRSchedulerConfig`: The configuration for the learning rate scheduler, including the scheduler type, parameters, etc.
+
+Example:
+
+```python
+from refiners.training_utils import BaseConfig, TrainingConfig, OptimizerConfig, LRSchedulerConfig, Optimizers, LRSchedulers
+
+class AutoencoderConfig(BaseConfig):
+    # Since we are using a synthetic dataset, we will use a arbitrary fixed epoch size.
+    epoch_size: int = 2048
+
+training = TrainingConfig(
+    duration="1000:epoch",
+    batch_size=32,
+    device="cuda" if torch.cuda.is_available() else "cpu",
+    dtype="float32"
+)
+
+optimizer = OptimizerConfig(
+    optimizer=Optimizers.AdamW,
+    learning_rate=1e-4,
+)
+
+lr_scheduler = LRSchedulerConfig(
+    type=LRSchedulers.ConstantLR
+)
+
+config = AutoencoderConfig(
+    training=training,
+    optimizer=optimizer,
+    lr_scheduler=lr_scheduler,
+)
+```
+
+### Subclass
+
+We can now define the Trainer subclass. It should inherit from `refiners.training_utils.Trainer` and implement the following methods:
+
+  - `get_item`: This method should take an index and return a Batch.
+  - `collate_fn`: This method should take a list of Batch and return a concatenated Batch.
+  - `dataset_length`: We implement this property to return the length of the dataset.
+  - `compute_loss`: This method should take a Batch and return the loss.
+
+```python
+from functools import cached_property
+from refiners.training_utils import Trainer
+
+
+class AutoencoderTrainer(Trainer[AutoencoderConfig, Batch]):
+    @cached_property
+    def image_generator(self) -> Generator[torch.Tensor, None, None]:
+        return generate_mask(size=64)
+
+    def get_item(self, index: int) -> Batch:
+        return Batch(image=next(self.image_generator).to(self.device, self.dtype))
+
+    def collate_fn(self, batch: list[Batch]) -> Batch:
+        return Batch(image=torch.cat([b.image for b in batch]))
+
+    @property
+    def dataset_length(self) -> int:
+        return self.config.epoch_size
+
+    def compute_loss(self, batch: Batch) -> torch.Tensor:
+        raise NotImplementedError("We'll implement this later")
+
+
+trainer = AutoencoderTrainer(config)
+```
+
+### Model registration
+
+For the Trainer to be able to handle the model, we need to register it. 
+
+We need two things to do so: 
+
+ - Add `refiners.training_utils.ModelConfig` attribute to the Config named `autoencoder`.
+ - Add a method to the Trainer subclass that returns the model decorated with `@register_model` decorator. This method should take the `ModelConfig` as an argument. The Trainer's `__init__` will register the models and add any parameters to the optimizer that have `requires_grad` enabled.
+
+After registering the model, the `self.autoencoder` attribute will be available in the Trainer.
+
+```python
+from refiners.training_utils import ModelConfig, register_model
+
+
+class AutoencoderModelConfig(ModelConfig):
+    pass
+
+
+class AutoencoderConfig(BaseConfig):
+    epoch_size: int = 2048
+    autoencoder: AutoencoderModelConfig
+
+
+class AutoencoderTrainer(Trainer[AutoencoderConfig, Batch]):
+    @register_model()
+    def autoencoder(self, config: AutoencoderModelConfig) -> Autoencoder:
+        return Autoencoder()
+
+    def compute_loss(self, batch: Batch) -> torch.Tensor:
+        x_reconstructed = self.autoencoder.decoder(
+            self.autoencoder.encoder(batch.image)
+        )
+        return F.binary_cross_entropy(x_reconstructed, batch.image)
+```
+
+We now have a fully functional Trainer that can train our autoencoder. We can now call the `train` method to start the training loop.
+
+```python
+trainer.train()
+```
+
+![alt text](terminal-logging.png)
+
+
+## Evaluation
+
+We can also evaluate the model using the `compute_evaluation` method.
+
+```python
+training = TrainingConfig(
+    duration="1000:epoch",
+    batch_size=32,
+    device="cuda" if torch.cuda.is_available() else "cpu",
+    dtype="float32",
+    evaluation_interval="50:epoch" # We set the evaluation to be done every 10 epochs
+)
+
+class AutoencoderTrainer(Trainer[AutoencoderConfig, Batch]):
+    # ... other methods
+
+    def compute_evaluation(self) -> None:
+        generator = generate_mask(size=64, seed=0)
+
+        grid: list[tuple[Image.Image, Image.Image]] = []
+        for _ in range(4):
+            mask = next(generator).to(self.device, self.dtype)
+            x_reconstructed = self.autoencoder.decoder(
+                self.autoencoder.encoder(mask)
+            )
+            loss = F.mse_loss(x_reconstructed, mask)
+            logger.info(f"Validation loss: {loss.detach().cpu().item()}")
+            grid.append(
+                (tensor_to_image(mask), tensor_to_image((x_reconstructed>0.5).float()))
+            )
+
+        import matplotlib.pyplot as plt
+
+        _, axes = plt.subplots(4, 2, figsize=(8, 16))
+
+        for i, (mask, reconstructed) in enumerate(grid):
+            axes[i, 0].imshow(mask, cmap='gray')
+            axes[i, 0].axis('off')
+            axes[i, 0].set_title('Mask')
+
+            axes[i, 1].imshow(reconstructed, cmap='gray')
+            axes[i, 1].axis('off')
+            axes[i, 1].set_title('Reconstructed')
+
+        plt.tight_layout()
+        plt.savefig(f"result_{trainer.clock.epoch}.png")
+        plt.close()
+```
+
+![alt text](evaluation.png)
+
+
+## Logging
+
+Let's write a simple logging callback to log the loss and the reconstructed images during training. A callback is a class that inherits from `refiners.training_utils.Callback` and implement any of the following methods:
+
+- `on_init_begin`
+- `on_init_end`
+- `on_train_begin`
+- `on_train_end`
+- `on_epoch_begin`
+- `on_epoch_end`
+- `on_batch_begin`
+- `on_batch_end`
+- `on_backward_begin`
+- `on_backward_end`
+- `on_optimizer_step_begin`
+- `on_optimizer_step_end`
+- `on_compute_loss_begin`
+- `on_compute_loss_end`
+- `on_evaluate_begin`
+- `on_evaluate_end`
+- `on_lr_scheduler_step_begin`
+- `on_lr_scheduler_step_end`
+
+We will implement the `on_epoch_end` method to log the loss and the reconstructed images and the `on_compute_loss_end` method to store the loss in a list.
+
+```python
+from refiners.training_utils import Callback
+from loguru import logger
+from typing import Any
+
+
+class LoggingCallback(Callback[Any]):
+    losses: list[float] = []
+
+    def on_compute_loss_end(self, loss: torch.Tensor) -> None:
+        self.losses.append(loss.item())
+
+    def on_epoch_end(self, epoch: int) -> None:
+        mean_loss = sum(self.losses) / len(self.losses)
+        logger.info(f"Mean loss: {mean_loss}, epoch: {epoch}")
+        self.losses = []
+```
+
+Exactly like models, we need to register the callback to the Trainer. We can do so by adding a CallbackConfig attribute to the Config named `logging` and adding a method to the Trainer class that returns the callback decorated with `@register_callback` decorator. 
+
+```python
+from refiners.training_utils import CallbackConfig, register_callback
+
+class AutoencoderConfig(BaseConfig):
+    epoch_size: int = 2048
+    logging: CallbackConfig = CallbackConfig()
+
+
+class AutoencoderTrainer(Trainer[AutoencoderConfig, Batch]):
+    # ... other methods
+
+    @register_callback()
+    def logging(self, config: CallbackConfig) -> LoggingCallback:
+        return LoggingCallback()
+```
+
+![alt text](loss-logging.png)
+
+??? complete end-to-end code "Expand to see the full code."
+
+    ```py
+    import random
+    from dataclasses import dataclass
+    from functools import cached_property
+    from typing import Any, Generator
+
+    import torch
+    from loguru import logger
+    from PIL import Image
+    from refiners.fluxion import layers as fl
+    from refiners.fluxion.utils import image_to_tensor, tensor_to_image
+    from refiners.training_utils import (
+        BaseConfig,
+        Callback,
+        CallbackConfig,
+        ClockConfig,
+        LRSchedulerConfig,
+        LRSchedulerType,
+        ModelConfig,
+        OptimizerConfig,
+        Optimizers,
+        Trainer,
+        TrainingConfig,
+        register_callback,
+        register_model,
+    )
+    from torch.nn import functional as F
+
+
+    class ConvBlock(fl.Chain):
+        def __init__(self, in_channels: int, out_channels: int) -> None:
+            super().__init__(
+                fl.Conv2d(
+                    in_channels=in_channels,
+                    out_channels=out_channels,
+                    kernel_size=3,
+                    padding=1,
+                    groups=min(in_channels, out_channels)
+                ),
+                fl.LayerNorm2d(out_channels),
+                fl.SiLU(),
+                fl.Conv2d(
+                    in_channels=out_channels,
+                    out_channels=out_channels,
+                    kernel_size=1,
+                    padding=0,
+                ),
+                fl.LayerNorm2d(out_channels),
+                fl.SiLU(),
+            )
+
+
+    class ResidualBlock(fl.Sum):
+        def __init__(self, in_channels: int, out_channels: int) -> None:
+            super().__init__(
+                ConvBlock(in_channels=in_channels, out_channels=out_channels),
+                fl.Conv2d(
+                    in_channels=in_channels,
+                    out_channels=out_channels,
+                    kernel_size=3,
+                    padding=1,
+                ),
+            )
+
+
+    class Encoder(fl.Chain):
+        def __init__(self) -> None:
+            super().__init__(
+                ResidualBlock(in_channels=1, out_channels=8),
+                fl.Downsample(channels=8, scale_factor=2, register_shape=False),
+                ResidualBlock(in_channels=8, out_channels=16),
+                fl.Downsample(channels=16, scale_factor=2, register_shape=False),
+                ResidualBlock(in_channels=16, out_channels=32),
+                fl.Downsample(channels=32, scale_factor=2, register_shape=False),
+                fl.Reshape(2048),
+                fl.Linear(in_features=2048, out_features=256),
+                fl.SiLU(),
+                fl.Linear(in_features=256, out_features=256),
+            )
+
+
+    class Decoder(fl.Chain):
+        def __init__(self) -> None:
+            super().__init__(
+                fl.Linear(in_features=256, out_features=256),
+                fl.SiLU(),
+                fl.Linear(in_features=256, out_features=2048),
+                fl.Reshape(32, 8, 8),
+                ResidualBlock(in_channels=32, out_channels=32),
+                ResidualBlock(in_channels=32, out_channels=32),
+                fl.Upsample(channels=32, upsample_factor=2),
+                ResidualBlock(in_channels=32, out_channels=16),
+                ResidualBlock(in_channels=16, out_channels=16),
+                fl.Upsample(channels=16, upsample_factor=2),
+                ResidualBlock(in_channels=16, out_channels=8),
+                ResidualBlock(in_channels=8, out_channels=8),
+                fl.Upsample(channels=8, upsample_factor=2),
+                ResidualBlock(in_channels=8, out_channels=8),
+                ResidualBlock(in_channels=8, out_channels=1),
+                fl.Sigmoid(),
+            )
+
+
+    class Autoencoder(fl.Chain):
+        def __init__(self) -> None:
+            super().__init__(
+                Encoder(),
+                Decoder(),
+            )
+
+        @property
+        def encoder(self) -> Encoder:
+            return self.ensure_find(Encoder)
+
+        @property
+        def decoder(self) -> Decoder:
+            return self.ensure_find(Decoder)
+
+
+    def generate_mask(size: int, seed: int | None = None) -> Generator[torch.Tensor, None, None]:
+        """Generate a tensor of a binary mask of size `size` using random rectangles."""
+        if seed is None:
+            seed = random.randint(0, 2**32 - 1)
+        random.seed(seed)
+
+        while True:
+            rectangle = Image.new(
+                "L", (random.randint(1, size), random.randint(1, size)), color=255
+            )
+            mask = Image.new("L", (size, size))
+            mask.paste(
+                rectangle,
+                (
+                    random.randint(0, size - rectangle.width),
+                    random.randint(0, size - rectangle.height),
+                ),
+            )
+            tensor = image_to_tensor(mask)
+
+            if random.random() > 0.5:
+                tensor = 1 - tensor
+
+            yield tensor
+
+
+    @dataclass
+    class Batch:
+        image: torch.Tensor
+
+
+    class AutoencoderModelConfig(ModelConfig):
+        pass
+
+
+    class LoggingCallback(Callback[Trainer[Any, Any]]):
+        losses: list[float] = []
+
+        def on_compute_loss_end(self, trainer: Trainer[Any, Any]) -> None:
+            self.losses.append(trainer.loss.detach().cpu().item())
+
+        def on_epoch_end(self, trainer: Trainer[Any, Any]) -> None:
+            mean_loss = sum(self.losses) / len(self.losses)
+            logger.info(f"Mean loss: {mean_loss}, epoch: {trainer.clock.epoch}")
+            self.losses = []
+
+
+    class AutoencoderConfig(BaseConfig):
+        epoch_size: int = 2048
+        autoencoder: AutoencoderModelConfig
+        logging: CallbackConfig = CallbackConfig()
+
+
+    autoencoder_config = AutoencoderModelConfig(
+        requires_grad=True,  # set during registration to set the requires_grad attribute of the model.
+    )
+
+    training = TrainingConfig(
+        duration="1000:epoch",  # type: ignore
+        batch_size=32,
+        device="cuda" if torch.cuda.is_available() else "cpu",
+        dtype="float32",
+        evaluation_interval="50:epoch",  # type: ignore
+    )
+
+    optimizer = OptimizerConfig(
+        optimizer=Optimizers.AdamW,
+        learning_rate=1e-4,
+    )
+
+    lr_scheduler = LRSchedulerConfig(
+        type=LRSchedulerType.CONSTANT_LR
+    )
+
+    config = AutoencoderConfig(
+        training=training,
+        optimizer=optimizer,
+        lr_scheduler=lr_scheduler,
+        autoencoder=autoencoder_config,
+        clock=ClockConfig(verbose=False),  # to disable the default clock logging
+    )
+
+
+    class AutoencoderTrainer(Trainer[AutoencoderConfig, Batch]):
+        @cached_property
+        def image_generator(self) -> Generator[torch.Tensor, None, None]:
+            return generate_mask(size=64)
+
+        def get_item(self, index: int) -> Batch:
+            return Batch(image=next(self.image_generator).to(self.device, self.dtype))
+
+        def collate_fn(self, batch: list[Batch]) -> Batch:
+            return Batch(image=torch.cat([b.image for b in batch]))
+
+        @property
+        def dataset_length(self) -> int:
+            return self.config.epoch_size
+
+        @register_model()
+        def autoencoder(self, config: AutoencoderModelConfig) -> Autoencoder:
+            return Autoencoder()
+
+        def compute_loss(self, batch: Batch) -> torch.Tensor:
+            x_reconstructed = self.autoencoder.decoder(
+                self.autoencoder.encoder(batch.image)
+            )
+            return F.binary_cross_entropy(x_reconstructed, batch.image)
+
+        def compute_evaluation(self) -> None:
+            generator = generate_mask(size=64, seed=0)
+
+            grid: list[tuple[Image.Image, Image.Image]] = []
+            validation_losses: list[float] = []
+            for _ in range(4):
+                mask = next(generator).to(self.device, self.dtype)
+                x_reconstructed = self.autoencoder.decoder(self.autoencoder.encoder(mask))
+                loss = F.mse_loss(x_reconstructed, mask)
+                validation_losses.append(loss.detach().cpu().item())
+                grid.append((tensor_to_image(mask), tensor_to_image((x_reconstructed>0.5).float())))
+
+            mean_loss = sum(validation_losses) / len(validation_losses)
+            logger.info(f"Mean validation loss: {mean_loss}, epoch: {self.clock.epoch}")
+
+            import matplotlib.pyplot as plt
+
+            _, axes = plt.subplots(4, 2, figsize=(8, 16)) # type: ignore
+
+            for i, (mask, reconstructed) in enumerate(grid):
+                axes[i, 0].imshow(mask, cmap="gray")
+                axes[i, 0].axis("off")
+                axes[i, 0].set_title("Mask")
+
+                axes[i, 1].imshow(reconstructed, cmap="gray")
+                axes[i, 1].axis("off")
+                axes[i, 1].set_title("Reconstructed")
+
+            plt.tight_layout()
+            plt.savefig(f"result_{trainer.clock.epoch}.png")  # type: ignore
+            plt.close()
+
+        @register_callback()
+        def logging(self, config: CallbackConfig) -> LoggingCallback:
+            return LoggingCallback()
+
+
+    trainer = AutoencoderTrainer(config)
+
+    trainer.train()
+
+    ```

mkdocs.yml

@@ -67,6 +67,7 @@ nav:
     - concepts/adapter/index.md
   - Guides:
     - Adapting SDXL: guides/adapting_sdxl/index.md
+    - Training 101: guides/training_101/index.md
   - API Reference:
       - Refiners: reference/
 extra: