code: def _alpha(t, s=0.008):
      return np.exp(
          np.log(np.cos(np.pi / 2 * (t + s) / (1 + s)))
          - np.log(np.cos(np.pi / 2 * (s) / (1 + s)))
      )
  
file_path: diffusion-for-beginners/samplers/dpm_solver.py
imports: import torch
  import numpy
label_desc: Use image node_id 3 for calling the DPMSampler obj's underlying member method code with example usage: obj._alpha(t, s) and returns: np