LMSDiscreteScheduler

LMSDiscreteScheduler is a linear multistep scheduler for discrete beta schedules. The scheduler is ported from and created by Katherine Crowson, and the original implementation can be found at crowsonkb/k-diffusion.

LMSDiscreteScheduler

class diffusers.LMSDiscreteScheduler

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( num_train_timesteps: int = 1000 beta_start: float = 0.0001 beta_end: float = 0.02 beta_schedule: str = 'linear' trained_betas: typing.Union[numpy.ndarray, typing.List[float], NoneType] = None use_karras_sigmas: typing.Optional[bool] = False use_exponential_sigmas: typing.Optional[bool] = False use_beta_sigmas: typing.Optional[bool] = False prediction_type: str = 'epsilon' timestep_spacing: str = 'linspace' steps_offset: int = 0 )

Parameters

num_train_timesteps (int, defaults to 1000) — The number of diffusion steps to train the model.
beta_start (float, defaults to 0.0001) — The starting beta value of inference.
beta_end (float, defaults to 0.02) — The final beta value.
beta_schedule (str, defaults to "linear") — The beta schedule, a mapping from a beta range to a sequence of betas for stepping the model. Choose from linear or scaled_linear.
trained_betas (np.ndarray, optional) — Pass an array of betas directly to the constructor to bypass beta_start and beta_end.
use_karras_sigmas (bool, optional, defaults to False) — Whether to use Karras sigmas for step sizes in the noise schedule during the sampling process. If True, the sigmas are determined according to a sequence of noise levels {σi}.
use_exponential_sigmas (bool, optional, defaults to False) — Whether to use exponential sigmas for step sizes in the noise schedule during the sampling process.
use_beta_sigmas (bool, optional, defaults to False) — Whether to use beta sigmas for step sizes in the noise schedule during the sampling process. Refer to Beta Sampling is All You Need for more information.
prediction_type (str, defaults to epsilon, optional) — Prediction type of the scheduler function; can be epsilon (predicts the noise of the diffusion process), sample (directly predicts the noisy sample) or v_prediction` (see section 2.4 of Imagen Video paper).
timestep_spacing (str, defaults to "linspace") — The way the timesteps should be scaled. Refer to Table 2 of the Common Diffusion Noise Schedules and Sample Steps are Flawed for more information.
steps_offset (int, defaults to 0) — An offset added to the inference steps, as required by some model families.

A linear multistep scheduler for discrete beta schedules.

This model inherits from SchedulerMixin and ConfigMixin. Check the superclass documentation for the generic methods the library implements for all schedulers such as loading and saving.

get_lms_coefficient

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( order t current_order )

Parameters

order () —
t () —
current_order () —

Compute the linear multistep coefficient.

scale_model_input

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( sample: Tensor timestep: typing.Union[float, torch.Tensor] ) → torch.Tensor

Parameters

sample (torch.Tensor) — The input sample.
timestep (float or torch.Tensor) — The current timestep in the diffusion chain.

Returns

torch.Tensor

A scaled input sample.

Ensures interchangeability with schedulers that need to scale the denoising model input depending on the current timestep.

set_begin_index

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( begin_index: int = 0 )

Parameters

begin_index (int) — The begin index for the scheduler.

Sets the begin index for the scheduler. This function should be run from pipeline before the inference.

set_timesteps

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( num_inference_steps: int device: typing.Union[str, torch.device] = None )

Parameters

num_inference_steps (int) — The number of diffusion steps used when generating samples with a pre-trained model.
device (str or torch.device, optional) — The device to which the timesteps should be moved to. If None, the timesteps are not moved.

Sets the discrete timesteps used for the diffusion chain (to be run before inference).

step

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( model_output: Tensor timestep: typing.Union[float, torch.Tensor] sample: Tensor order: int = 4 return_dict: bool = True ) → SchedulerOutput or tuple

Parameters

model_output (torch.Tensor) — The direct output from learned diffusion model.
timestep (float or torch.Tensor) — The current discrete timestep in the diffusion chain.
sample (torch.Tensor) — A current instance of a sample created by the diffusion process.
order (int, defaults to 4) — The order of the linear multistep method.
return_dict (bool, optional, defaults to True) — Whether or not to return a SchedulerOutput or tuple.

Returns

SchedulerOutput or tuple

If return_dict is True, SchedulerOutput is returned, otherwise a tuple is returned where the first element is the sample tensor.

Predict the sample from the previous timestep by reversing the SDE. This function propagates the diffusion process from the learned model outputs (most often the predicted noise).