code: def _mean(self, x0, t, y):
      b0, b1, s = self.beta_min, self.beta_max, self.stiffness
      x0y_fac = torch.exp(-0.25 * s * t * (t * (b1 - b0) + 2 * b0))[
          :, None, None, None
      ]
      return y + x0y_fac * (x0 - y)
  
imports: import abc
  import warnings
  import numpy
  import torch
label_desc: Use image node_id 6 for calling the OUVPSDE obj's underlying member method code with example usage: obj._mean(x0, t, y) and returns: unknown