add the UniPC scheduler (#2373)

* add UniPC scheduler

* add the return type to the functions

* code quality check

* add tests

* finish docs

---------

Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

docs/source/en/_toctree.yml

@@ -148,7 +148,7 @@
       - local: api/pipelines/stable_diffusion/upscale
         title: Super-Resolution
       - local: api/pipelines/stable_diffusion/latent_upscale
-        title: Stable-Diffusion-Latent-Upscaler  
+        title: Stable-Diffusion-Latent-Upscaler
       - local: api/pipelines/stable_diffusion/pix2pix
         title: InstructPix2Pix
       - local: api/pipelines/stable_diffusion/pix2pix_zero
@@ -204,6 +204,8 @@
       title: Singlestep DPM-Solver
     - local: api/schedulers/stochastic_karras_ve
       title: Stochastic Kerras VE
+    - local: api/schedulers/unipc
+      title: UniPCMultistepScheduler
     - local: api/schedulers/score_sde_ve
       title: VE-SDE
     - local: api/schedulers/score_sde_vp

docs/source/en/api/schedulers/overview.mdx

@@ -43,11 +43,11 @@ To this end, the design of schedulers is such that:
 
 The following table summarizes all officially supported schedulers, their corresponding paper
 
-
 | Scheduler | Paper |
 |---|---|
 | [ddim](./ddim) | [**Denoising Diffusion Implicit Models**](https://arxiv.org/abs/2010.02502) |
 | [ddpm](./ddpm) | [**Denoising Diffusion Probabilistic Models**](https://arxiv.org/abs/2006.11239) |
+| [deis](./deis) | [**DEISMultistepScheduler**](https://arxiv.org/abs/2204.13902) |
 | [singlestep_dpm_solver](./singlestep_dpm_solver) | [**Singlestep DPM-Solver**](https://arxiv.org/abs/2206.00927) |
 | [multistep_dpm_solver](./multistep_dpm_solver) | [**Multistep DPM-Solver**](https://arxiv.org/abs/2206.00927) |
 | [heun](./heun) | [**Heun scheduler inspired by Karras et. al paper**](https://arxiv.org/abs/2206.00364) |
@@ -62,6 +62,7 @@ The following table summarizes all officially supported schedulers, their corres
 | [euler](./euler) | [**Euler scheduler**](https://arxiv.org/abs/2206.00364) |
 | [euler_ancestral](./euler_ancestral) | [**Euler Ancestral scheduler**](https://github.com/crowsonkb/k-diffusion/blob/481677d114f6ea445aa009cf5bd7a9cdee909e47/k_diffusion/sampling.py#L72) |
 | [vq_diffusion](./vq_diffusion) | [**VQDiffusionScheduler**](https://arxiv.org/abs/2111.14822) |
+| [unipc](./unipc) | [**UniPCMultistepScheduler**](https://arxiv.org/abs/2302.04867) |
 | [repaint](./repaint) | [**RePaint scheduler**](https://arxiv.org/abs/2201.09865) |
 
 ## API

docs/source/en/api/schedulers/unipc.mdx

@@ -0,0 +1,24 @@
+<!--Copyright 2022 The HuggingFace Team. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+the License. You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+specific language governing permissions and limitations under the License.
+-->
+
+# UniPC
+
+## Overview
+
+UniPC is a training-free framework designed for the fast sampling of diffusion models, which consists of a corrector (UniC) and a predictor (UniP) that share a unified analytical form and support arbitrary orders.
+
+For more details about the method, please refer to the [[paper]](https://arxiv.org/abs/2302.04867) and the [[code]](https://github.com/wl-zhao/UniPC).
+
+Fast Sampling of Diffusion Models with Exponential Integrator.
+
+## UniPCMultistepScheduler
+[[autodoc]] UniPCMultistepScheduler