class_docstr: Utilities for training and sampling diffusion models.
  
  Ported directly from here, and then adapted over time to further experimentation.
  https://github.com/hojonathanho/diffusion/blob/1e0dceb3b3495bbe19116a5e1b3596cd0706c543/diffusion_tf/diffusion_utils_2.py#L42
  
  :param betas: a 1-D numpy array of betas for each diffusion timestep,
                starting at T and going to 1.
  :param model_mean_type: a ModelMeanType determining what the model outputs.
  :param model_var_type: a ModelVarType determining how variance is output.
  :param loss_type: a LossType determining the loss function to use.
  :param rescale_timesteps: if True, pass floating point timesteps into the
                            model so that they are always scaled like in the
                            original paper (0 to 1000).
class_docstr_tok: ["Utilities","for","training","and","sampling","diffusion","models",".","Ported","directly","from","here",",","and","then","adapted","over","time","to","further","experimentation",".","https",":","\/\/github.com\/hojonathanho\/diffusion\/blob\/1e0dceb3b3495bbe19116a5e1b3596cd0706c543\/diffusion_tf\/diffusion_utils_2.py","#","L42",":","param","betas",":","a","1-D","numpy","array","of","betas","for","each","diffusion","timestep",",","starting","at","T","and","going","to","1.",":","param","model_mean_type",":","a","ModelMeanType","determining","what","the","model","outputs",".",":","param","model_var_type",":","a","ModelVarType","determining","how","variance","is","output",".",":","param","loss_type",":","a","LossType","determining","the","loss","function","to","use",".",":","param","rescale_timesteps",":","if","True",",","pass","floating","point","timesteps","into","the","model","so","that","they","are","always","scaled","like","in","the","original","paper","(","0","to","1000",")","."]
code: def _predict_xstart_from_xprev(self, x_t, t, xprev):
      assert x_t.shape == xprev.shape
      return (  # (xprev - coef2*x_t) / coef1
          _extract_into_tensor(
              1.0 / self.posterior_mean_coef1, t, x_t.shape
          )
          * xprev
          - _extract_into_tensor(
              self.posterior_mean_coef2 / self.posterior_mean_coef1,
              t,
              x_t.shape,
          )
          * x_t
      )
  
imports: import enum
  import math
  import numpy
  import torch
  import torch
  from tqdm import tqdm
  from TTS.tts.layers.tortoise.dpm_solver import DPM_Solver, NoiseScheduleVP, model_wrapper
label_desc: Use image node_id 7 for calling the GaussianDiffusion obj's underlying member method code with example usage: obj._predict_xstart_from_xprev(x_t, t, xprev) and returns: unknown