the current timestep.   prev_timestep (int) —
The previous discrete timestep in the diffusion chain.   sample (torch.FloatTensor) —
A current instance of a sample created by the diffusion process.   order (int) —
The order of UniP at this timestep (corresponds to the p in UniPC-p).   Returns 
torch.FloatTensor
  
The sample tensor at the previous timestep.
  One step for the UniP (B(h) version). Alternatively, self.solver_p is used if is specif