(doc/fluxion/ld) add Solver docstrings

src/refiners/foundationals/latent_diffusion/solvers/solver.py

@@ -10,16 +10,23 @@ T = TypeVar("T", bound="Solver")
 
 
 class NoiseSchedule(str, Enum):
+    """An enumeration of noise schedules used to sample the noise schedule.
+
+    Attributes:
+        UNIFORM: A uniform noise schedule.
+        QUADRATIC: A quadratic noise schedule.
+        KARRAS: See [[arXiv:2206.00364] Elucidating the Design Space of Diffusion-Based Generative Models, Equation 5](https://arxiv.org/abs/2206.00364)
+    """
+
     UNIFORM = "uniform"
     QUADRATIC = "quadratic"
     KARRAS = "karras"
 
 
 class Solver(fl.Module, ABC):
-    """
+    """The base class for creating a diffusion model solver.
-    A base class for creating a diffusion model solver.
 
-    Solver creates a sequence of noise and scaling factors used in the diffusion process,
+    Solvers create a sequence of noise and scaling factors used in the diffusion process,
     which gradually transforms the original data distribution into a Gaussian one.
 
     This process is described using several parameters such as initial and final diffusion rates,
@@ -39,6 +46,18 @@ class Solver(fl.Module, ABC):
         device: Device | str = "cpu",
         dtype: DType = float32,
     ) -> None:
+        """Initializes a new `Solver` instance.
+
+        Args:
+            num_inference_steps: The number of inference steps to perform.
+            num_train_timesteps: The number of timesteps used to train the diffusion process.
+            initial_diffusion_rate: The initial diffusion rate used to sample the noise schedule.
+            final_diffusion_rate: The final diffusion rate used to sample the noise schedule.
+            noise_schedule: The noise schedule used to sample the noise schedule.
+            first_inference_step: The first inference step to perform.
+            device: The PyTorch device to use for the solver's tensors.
+            dtype: The PyTorch data type to use for the solver's tensors.
+        """
         super().__init__()
         self.num_inference_steps = num_inference_steps
         self.num_train_timesteps = num_train_timesteps
@@ -55,18 +74,24 @@ class Solver(fl.Module, ABC):
 
     @abstractmethod
     def __call__(self, x: Tensor, predicted_noise: Tensor, step: int, generator: Generator | None = None) -> Tensor:
-        """
+        """Apply a step of the diffusion process using the Solver.
-        Applies a step of the diffusion process to the input tensor `x` using the provided `predicted_noise` and `timestep`.
 
+        Note:
             This method should be overridden by subclasses to implement the specific diffusion process.
+
+        Args:
+            x: The input tensor to apply the diffusion process to.
+            predicted_noise: The predicted noise tensor for the current step.
+            step: The current step of the diffusion process.
+            generator: The random number generator to use for sampling noise.
         """
         ...
 
     @abstractmethod
     def _generate_timesteps(self) -> Tensor:
-        """
+        """Generate a tensor of timesteps.
-        Generates a tensor of timesteps.
 
+        Note:
             This method should be overridden by subclasses to provide the specific timesteps for the diffusion process.
         """
         ...
@@ -77,6 +102,16 @@ class Solver(fl.Module, ABC):
         noise: Tensor,
         step: int,
     ) -> Tensor:
+        """Add noise to the input tensor using the solver's parameters.
+
+        Args:
+            x: The input tensor to add noise to.
+            noise: The noise tensor to add to the input tensor.
+            step: The current step of the diffusion process.
+
+        Returns:
+            The input tensor with added noise.
+        """
         timestep = self.timesteps[step]
         cumulative_scale_factors = self.cumulative_scale_factors[timestep]
         noise_stds = self.noise_std[timestep]
@@ -84,28 +119,43 @@ class Solver(fl.Module, ABC):
         return noised_x
 
     def remove_noise(self, x: Tensor, noise: Tensor, step: int) -> Tensor:
+        """Remove noise from the input tensor using the current step of the diffusion process.
+
+        Args:
+            x: The input tensor to remove noise from.
+            noise: The noise tensor to remove from the input tensor.
+            step: The current step of the diffusion process.
+
+        Returns:
+            The denoised input tensor.
+        """
         timestep = self.timesteps[step]
         cumulative_scale_factors = self.cumulative_scale_factors[timestep]
         noise_stds = self.noise_std[timestep]
-        # See equation (15) from https://arxiv.org/pdf/2006.11239.pdf. Useful to preview progress or for guidance like
+        # See equation (15) from https://arxiv.org/pdf/2006.11239.pdf.
-        # in https://arxiv.org/pdf/2210.00939.pdf (self-attention guidance)
+        # Useful to preview progress or for guidance
+        # See also https://arxiv.org/pdf/2210.00939.pdf (self-attention guidance)
         denoised_x = (x - noise_stds * noise) / cumulative_scale_factors
         return denoised_x
 
     @property
     def all_steps(self) -> list[int]:
+        """Return a list of all inference steps."""
         return list(range(self.num_inference_steps))
 
     @property
     def inference_steps(self) -> list[int]:
+        """Return a list of inference steps to perform."""
         return self.all_steps[self.first_inference_step :]
 
     @property
     def device(self) -> Device:
+        """The PyTorch device used for the solver's tensors."""
         return self.scale_factors.device
 
     @property
     def dtype(self) -> DType:
+        """The PyTorch data type used for the solver's tensors."""
         return self.scale_factors.dtype
 
     @device.setter
@@ -117,6 +167,15 @@ class Solver(fl.Module, ABC):
         self.to(dtype=dtype)
 
     def rebuild(self: T, num_inference_steps: int | None, first_inference_step: int | None = None) -> T:
+        """Rebuild the solver with new parameters.
+
+        Args:
+            num_inference_steps: The number of inference steps to perform.
+            first_inference_step: The first inference step to perform.
+
+        Returns:
+            A new solver instance with the specified parameters.
+        """
         num_inference_steps = self.num_inference_steps if num_inference_steps is None else num_inference_steps
         first_inference_step = self.first_inference_step if first_inference_step is None else first_inference_step
         return self.__class__(
@@ -131,12 +190,30 @@ class Solver(fl.Module, ABC):
         )
 
     def scale_model_input(self, x: Tensor, step: int) -> Tensor:
-        """
+        """Scale the model's input according to the current timestep.
-        For compatibility with solvers that need to scale the input according to the current timestep.
+
+        Note:
+            This method should only be overridden by solvers that
+            need to scale the input according to the current timestep.
+
+        Args:
+            x: The input tensor to scale.
+            step: The current step of the diffusion process.
+
+        Returns:
+            The scaled input tensor.
         """
         return x
 
     def sample_power_distribution(self, power: float = 2, /) -> Tensor:
+        """Sample a power distribution.
+
+        Args:
+            power: The power to use for the distribution.
+
+        Returns:
+            A tensor representing the power distribution between the initial and final diffusion rates of the solver.
+        """
         return (
             linspace(
                 start=self.initial_diffusion_rate ** (1 / power),
@@ -147,6 +224,11 @@ class Solver(fl.Module, ABC):
         )
 
     def sample_noise_schedule(self) -> Tensor:
+        """Sample the noise schedule.
+
+        Returns:
+            A tensor representing the noise schedule.
+        """
         match self.noise_schedule:
             case "uniform":
                 return 1 - self.sample_power_distribution(1)
@@ -158,6 +240,15 @@ class Solver(fl.Module, ABC):
                 raise ValueError(f"Unknown noise schedule: {self.noise_schedule}")
 
     def to(self, device: Device | str | None = None, dtype: DType | None = None) -> "Solver":
+        """Move the solver to the specified device and data type.
+
+        Args:
+            device: The PyTorch device to move the solver to.
+            dtype: The PyTorch data type to move the solver to.
+
+        Returns:
+            The solver instance, moved to the specified device and data type.
+        """
         super().to(device=device, dtype=dtype)
         for name, attr in [(name, attr) for name, attr in self.__dict__.items() if isinstance(attr, Tensor)]:
             match name: