(doc/fluxion/ld) add DDPM, DDIM, DPM++ and Euleur docstrings

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

@@ -4,6 +4,11 @@ from refiners.foundationals.latent_diffusion.solvers.solver import NoiseSchedule
 
 
 class DDIM(Solver):
+    """Denoising Diffusion Implicit Model (DDIM) solver.
+
+    See [[arXiv:2010.02502] Denoising Diffusion Implicit Models](https://arxiv.org/abs/2010.02502) for more details.
+    """
+
     def __init__(
         self,
         num_inference_steps: int,
@@ -15,6 +20,18 @@ class DDIM(Solver):
         device: Device | str = "cpu",
         dtype: Dtype = float32,
     ) -> None:
+        """Initializes a new DDIM solver.
+
+        Args:
+            num_inference_steps: The number of inference steps.
+            num_train_timesteps: The number of training timesteps.
+            initial_diffusion_rate: The initial diffusion rate.
+            final_diffusion_rate: The final diffusion rate.
+            noise_schedule: The noise schedule.
+            first_inference_step: The first inference step.
+            device: The PyTorch device to use.
+            dtype: The PyTorch data type to use.
+        """
         super().__init__(
             num_inference_steps=num_inference_steps,
             num_train_timesteps=num_train_timesteps,

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

@@ -1,13 +1,16 @@
-from torch import Generator, Tensor, arange, device as Device, dtype as DType
+from torch import Generator, Tensor, arange, device as Device
 
-from refiners.foundationals.latent_diffusion.solvers.solver import NoiseSchedule, Solver
+from refiners.foundationals.latent_diffusion.solvers.solver import Solver
 
 
 class DDPM(Solver):
-    """
-    Denoising Diffusion Probabilistic Model
+    """Denoising Diffusion Probabilistic Model (DDPM) solver.
 
-    Only used for training Latent Diffusion models. Cannot be called.
+    Warning:
+        Only used for training Latent Diffusion models.
+        Cannot be called.
+
+    See [[arXiv:2006.11239] Denoising Diffusion Probabilistic Models](https://arxiv.org/abs/2006.11239) for more details.
     """
 
     def __init__(
@@ -16,11 +19,19 @@ class DDPM(Solver):
         num_train_timesteps: int = 1_000,
         initial_diffusion_rate: float = 8.5e-4,
         final_diffusion_rate: float = 1.2e-2,
-        noise_schedule: NoiseSchedule | None = None,  # ignored
         first_inference_step: int = 0,
         device: Device | str = "cpu",
-        dtype: DType | None = None,  # ignored
     ) -> None:
+        """Initializes a new DDPM solver.
+
+        Args:
+            num_inference_steps: The number of inference steps.
+            num_train_timesteps: The number of training timesteps.
+            initial_diffusion_rate: The initial diffusion rate.
+            final_diffusion_rate: The final diffusion rate.
+            first_inference_step: The first inference step.
+            device: The PyTorch device to use.
+        """
         super().__init__(
             num_inference_steps=num_inference_steps,
             num_train_timesteps=num_train_timesteps,

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

@@ -7,13 +7,16 @@ from refiners.foundationals.latent_diffusion.solvers.solver import NoiseSchedule
 
 
 class DPMSolver(Solver):
-    """
-    Implements DPM-Solver++ from https://arxiv.org/abs/2211.01095
+    """Diffusion probabilistic models (DPMs) solver.
 
-    Regarding last_step_first_order: DPM-Solver++ is known to introduce artifacts
-    when used with SDXL and few steps. This parameter is a way to mitigate that
-    effect by using a first-order (Euler) update instead of a second-order update
-    for the last step of the diffusion.
+    See [[arXiv:2211.01095] DPM-Solver++: Fast Solver for Guided Sampling of Diffusion Probabilistic Models](https://arxiv.org/abs/2211.01095)
+    for more details.
+
+    Note:
+        Regarding last_step_first_order: DPM-Solver++ is known to introduce artifacts
+        when used with SDXL and few steps. This parameter is a way to mitigate that
+        effect by using a first-order (Euler) update instead of a second-order update
+        for the last step of the diffusion.
     """
 
     def __init__(
@@ -42,10 +45,16 @@ class DPMSolver(Solver):
         self.last_step_first_order = last_step_first_order
 
     def _generate_timesteps(self) -> Tensor:
-        # We need to use numpy here because:
-        # numpy.linspace(0,999,31)[15] is 499.49999999999994
-        # torch.linspace(0,999,31)[15] is 499.5
-        # ...and we want the same result as the original codebase.
+        """Generate the timesteps used by the solver.
+
+        Note:
+            We need to use numpy here because:
+
+            - numpy.linspace(0,999,31)[15] is 499.49999999999994
+            - torch.linspace(0,999,31)[15] is 499.5
+
+            and we want the same result as the original codebase.
+        """
         return tensor(
             np.linspace(0, self.num_train_timesteps - 1, self.num_inference_steps + 1).round().astype(int)[1:],
         ).flip(0)
@@ -55,6 +64,12 @@ class DPMSolver(Solver):
         num_inference_steps: int | None,
         first_inference_step: int | None = None,
     ) -> "DPMSolver":
+        """Rebuilds the solver with new parameters.
+
+        Args:
+            num_inference_steps: The number of inference steps.
+            first_inference_step: The first inference step.
+        """
         r = super().rebuild(
             num_inference_steps=num_inference_steps,
             first_inference_step=first_inference_step,
@@ -63,6 +78,16 @@ class DPMSolver(Solver):
         return r
 
     def dpm_solver_first_order_update(self, x: Tensor, noise: Tensor, step: int) -> Tensor:
+        """Applies a first-order backward Euler update to the input data `x`.
+
+        Args:
+            x: The input data.
+            noise: The predicted noise.
+            step: The current step.
+
+        Returns:
+            The denoised version of the input data `x`.
+        """
         current_timestep = self.timesteps[step]
         previous_timestep = self.timesteps[step + 1] if step < self.num_inference_steps - 1 else tensor([0])
 
@@ -79,6 +104,15 @@ class DPMSolver(Solver):
         return denoised_x
 
     def multistep_dpm_solver_second_order_update(self, x: Tensor, step: int) -> Tensor:
+        """Applies a second-order backward Euler update to the input data `x`.
+
+        Args:
+            x: The input data.
+            step: The current step.
+
+        Returns:
+            The denoised version of the input data `x`.
+        """
         previous_timestep = self.timesteps[step + 1] if step < self.num_inference_steps - 1 else tensor([0])
         current_timestep = self.timesteps[step]
         next_timestep = self.timesteps[step - 1]
@@ -106,12 +140,21 @@ class DPMSolver(Solver):
         return denoised_x
 
     def __call__(self, x: Tensor, predicted_noise: Tensor, step: int, generator: Generator | None = None) -> Tensor:
-        """
-        Represents one step of the backward diffusion process that iteratively denoises the input data `x`.
+        """Apply one step of the backward diffusion process.
 
-        This method works by estimating the denoised version of `x` and applying either a first-order or second-order
-        backward Euler update, which is a numerical method commonly used to solve ordinary differential equations
-        (ODEs).
+        Note:
+            This method works by estimating the denoised version of `x` and applying either a first-order or second-order
+            backward Euler update, which is a numerical method commonly used to solve ordinary differential equations
+            (ODEs).
+
+        Args:
+            x: The input data.
+            predicted_noise: The predicted noise.
+            step: The current step.
+            generator: The random number generator.
+
+        Returns:
+            The denoised version of the input data `x`.
         """
         assert self.first_inference_step <= step < self.num_inference_steps, "invalid step {step}"
 

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

@@ -6,6 +6,12 @@ from refiners.foundationals.latent_diffusion.solvers.solver import NoiseSchedule
 
 
 class Euler(Solver):
+    """Euler solver.
+
+    See [[arXiv:2206.00364] Elucidating the Design Space of Diffusion-Based Generative Models](https://arxiv.org/abs/2206.00364)
+    for more details.
+    """
+
     def __init__(
         self,
         num_inference_steps: int,
@@ -17,6 +23,18 @@ class Euler(Solver):
         device: Device | str = "cpu",
         dtype: Dtype = float32,
     ):
+        """Initializes a new Euler solver.
+
+        Args:
+            num_inference_steps: The number of inference steps.
+            num_train_timesteps: The number of training timesteps.
+            initial_diffusion_rate: The initial diffusion rate.
+            final_diffusion_rate: The final diffusion rate.
+            noise_schedule: The noise schedule.
+            first_inference_step: The first inference step.
+            device: The PyTorch device to use.
+            dtype: The PyTorch data type to use.
+        """
         if noise_schedule != NoiseSchedule.QUADRATIC:
             raise NotImplementedError
         super().__init__(
@@ -33,23 +51,40 @@ class Euler(Solver):
 
     @property
     def init_noise_sigma(self) -> Tensor:
+        """The initial noise sigma."""
         return self.sigmas.max()
 
     def _generate_timesteps(self) -> Tensor:
-        # We need to use numpy here because:
-        # numpy.linspace(0,999,31)[15] is 499.49999999999994
-        # torch.linspace(0,999,31)[15] is 499.5
-        # ...and we want the same result as the original codebase.
+        """Generate the timesteps used by the solver.
+
+        Note:
+            We need to use numpy here because:
+
+            - numpy.linspace(0,999,31)[15] is 499.49999999999994
+            - torch.linspace(0,999,31)[15] is 499.5
+
+            and we want the same result as the original codebase.
+        """
         timesteps = torch.tensor(np.linspace(0, self.num_train_timesteps - 1, self.num_inference_steps)).flip(0)
         return timesteps
 
     def _generate_sigmas(self) -> Tensor:
+        """Generate the sigmas used by the solver."""
         sigmas = self.noise_std / self.cumulative_scale_factors
         sigmas = torch.tensor(np.interp(self.timesteps.cpu().numpy(), np.arange(0, len(sigmas)), sigmas.cpu().numpy()))
         sigmas = torch.cat([sigmas, tensor([0.0])])
         return sigmas.to(device=self.device, dtype=self.dtype)
 
     def scale_model_input(self, x: Tensor, step: int) -> Tensor:
+        """Scales the model input according to the current step.
+
+        Args:
+            x: The model input.
+            step: The current step.
+
+        Returns:
+            The scaled model input.
+        """
         sigma = self.sigmas[step]
         return x / ((sigma**2 + 1) ** 0.5)