code: def get_variables(self, sigma, next_sigma, previous_sigma=None):
      t, t_next = [to_neg_log_sigma(s) for s in (sigma, next_sigma)]
      h = t_next - t
  
      if previous_sigma is not None:
          h_last = t - to_neg_log_sigma(previous_sigma)
          r = h_last / h
          return h, r, t, t_next
      else:
          return h, None, t, t_next
  
imports: from typing import Dict, Union
  import torch
  from omegaconf import ListConfig, OmegaConf
  from tqdm import tqdm
  from ...modules.diffusionmodules.sampling_utils import get_ancestral_step, linear_multistep_coeff, to_d, to_neg_log_sigma, to_sigma
  from ...util import append_dims, default, instantiate_from_config
label_desc: Use image node_id 1 for calling the DPMPP2MSampler obj's underlying member method code with example usage: obj.get_variables(sigma, next_sigma, previous_sigma) and returns: h,  r,  t,  t_next, h,  None,  t,  t_next