# KDPM2AncestralDiscreteScheduler

The `KDPM2DiscreteScheduler` with ancestral sampling is inspired by the [Elucidating the Design Space of Diffusion-Based Generative Models](https://huggingface.co/papers/2206.00364) paper, and the scheduler is ported from and created by [Katherine Crowson](https://github.com/crowsonkb/).

The original codebase can be found at [crowsonkb/k-diffusion](https://github.com/crowsonkb/k-diffusion).

## KDPM2AncestralDiscreteScheduler[[diffusers.KDPM2AncestralDiscreteScheduler]]
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<docstring><name>class diffusers.KDPM2AncestralDiscreteScheduler</name><anchor>diffusers.KDPM2AncestralDiscreteScheduler</anchor><source>https://github.com/huggingface/diffusers/blob/main/src/diffusers/schedulers/scheduling_k_dpm_2_ancestral_discrete.py#L96</source><parameters>[{"name": "num_train_timesteps", "val": ": int = 1000"}, {"name": "beta_start", "val": ": float = 0.00085"}, {"name": "beta_end", "val": ": float = 0.012"}, {"name": "beta_schedule", "val": ": str = 'linear'"}, {"name": "trained_betas", "val": ": typing.Union[numpy.ndarray, typing.List[float], NoneType] = None"}, {"name": "use_karras_sigmas", "val": ": typing.Optional[bool] = False"}, {"name": "use_exponential_sigmas", "val": ": typing.Optional[bool] = False"}, {"name": "use_beta_sigmas", "val": ": typing.Optional[bool] = False"}, {"name": "prediction_type", "val": ": str = 'epsilon'"}, {"name": "timestep_spacing", "val": ": str = 'linspace'"}, {"name": "steps_offset", "val": ": int = 0"}]</parameters><paramsdesc>- **num_train_timesteps** (`int`, defaults to 1000) --
  The number of diffusion steps to train the model.
- **beta_start** (`float`, defaults to 0.00085) --
  The starting `beta` value of inference.
- **beta_end** (`float`, defaults to 0.012) --
  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](https://huggingface.co/papers/2407.12173) 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](https://imagen.research.google/video/paper.pdf) 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](https://huggingface.co/papers/2305.08891) for more information.
- **steps_offset** (`int`, defaults to 0) --
  An offset added to the inference steps, as required by some model families.</paramsdesc><paramgroups>0</paramgroups></docstring>

KDPM2DiscreteScheduler with ancestral sampling is inspired by the DPMSolver2 and Algorithm 2 from the [Elucidating
the Design Space of Diffusion-Based Generative Models](https://huggingface.co/papers/2206.00364) paper.

This model inherits from [SchedulerMixin](/docs/diffusers/main/en/api/schedulers/overview#diffusers.SchedulerMixin) and [ConfigMixin](/docs/diffusers/main/en/api/configuration#diffusers.ConfigMixin). Check the superclass documentation for the generic
methods the library implements for all schedulers such as loading and saving.





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<docstring><name>scale_model_input</name><anchor>diffusers.KDPM2AncestralDiscreteScheduler.scale_model_input</anchor><source>https://github.com/huggingface/diffusers/blob/main/src/diffusers/schedulers/scheduling_k_dpm_2_ancestral_discrete.py#L214</source><parameters>[{"name": "sample", "val": ": Tensor"}, {"name": "timestep", "val": ": typing.Union[float, torch.Tensor]"}]</parameters><paramsdesc>- **sample** (`torch.Tensor`) --
  The input sample.
- **timestep** (`int`, *optional*) --
  The current timestep in the diffusion chain.</paramsdesc><paramgroups>0</paramgroups><rettype>`torch.Tensor`</rettype><retdesc>A scaled input sample.</retdesc></docstring>

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








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<docstring><name>set_begin_index</name><anchor>diffusers.KDPM2AncestralDiscreteScheduler.set_begin_index</anchor><source>https://github.com/huggingface/diffusers/blob/main/src/diffusers/schedulers/scheduling_k_dpm_2_ancestral_discrete.py#L204</source><parameters>[{"name": "begin_index", "val": ": int = 0"}]</parameters><paramsdesc>- **begin_index** (`int`) --
  The begin index for the scheduler.</paramsdesc><paramgroups>0</paramgroups></docstring>

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




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<docstring><name>set_timesteps</name><anchor>diffusers.KDPM2AncestralDiscreteScheduler.set_timesteps</anchor><source>https://github.com/huggingface/diffusers/blob/main/src/diffusers/schedulers/scheduling_k_dpm_2_ancestral_discrete.py#L244</source><parameters>[{"name": "num_inference_steps", "val": ": int"}, {"name": "device", "val": ": typing.Union[str, torch.device] = None"}, {"name": "num_train_timesteps", "val": ": typing.Optional[int] = None"}]</parameters><paramsdesc>- **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.</paramsdesc><paramgroups>0</paramgroups></docstring>

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




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<docstring><name>step</name><anchor>diffusers.KDPM2AncestralDiscreteScheduler.step</anchor><source>https://github.com/huggingface/diffusers/blob/main/src/diffusers/schedulers/scheduling_k_dpm_2_ancestral_discrete.py#L475</source><parameters>[{"name": "model_output", "val": ": typing.Union[torch.Tensor, numpy.ndarray]"}, {"name": "timestep", "val": ": typing.Union[float, torch.Tensor]"}, {"name": "sample", "val": ": typing.Union[torch.Tensor, numpy.ndarray]"}, {"name": "generator", "val": ": typing.Optional[torch._C.Generator] = None"}, {"name": "return_dict", "val": ": bool = True"}]</parameters><paramsdesc>- **model_output** (`torch.Tensor`) --
  The direct output from learned diffusion model.
- **timestep** (`float`) --
  The current discrete timestep in the diffusion chain.
- **sample** (`torch.Tensor`) --
  A current instance of a sample created by the diffusion process.
- **generator** (`torch.Generator`, *optional*) --
  A random number generator.
- **return_dict** (`bool`) --
  Whether or not to return a
  `KDPM2AncestralDiscreteSchedulerOutput` or tuple.</paramsdesc><paramgroups>0</paramgroups><rettype>`KDPM2AncestralDiscreteSchedulerOutput` or `tuple`</rettype><retdesc>If return_dict is `True`,
`KDPM2AncestralDiscreteSchedulerOutput` is
returned, otherwise a tuple is returned where the first element is the sample tensor.</retdesc></docstring>

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).








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## SchedulerOutput[[diffusers.schedulers.scheduling_utils.SchedulerOutput]]
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<docstring><name>class diffusers.schedulers.scheduling_utils.SchedulerOutput</name><anchor>diffusers.schedulers.scheduling_utils.SchedulerOutput</anchor><source>https://github.com/huggingface/diffusers/blob/main/src/diffusers/schedulers/scheduling_utils.py#L62</source><parameters>[{"name": "prev_sample", "val": ": Tensor"}]</parameters><paramsdesc>- **prev_sample** (`torch.Tensor` of shape `(batch_size, num_channels, height, width)` for images) --
  Computed sample `(x_{t-1})` of previous timestep. `prev_sample` should be used as next model input in the
  denoising loop.</paramsdesc><paramgroups>0</paramgroups></docstring>

Base class for the output of a scheduler's `step` function.




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