 UniC can be also applied
after any off-the-shelf solvers to increase the order of accuracy.
For more details, see the original paper: https://arxiv.org/abs/2302.04867
Currently, we support the multistep UniPC for both noise prediction models and data prediction models. We recommend
to use solver_order=2 for guided sampling, and solver_order=3 for unconditional sampling.
We also support the “dynamic thresholding” method in Imagen (https://arxiv