yellowfin.py 文件源码

def get_mu(self):
    coef = [-1.0, 3.0, 0.0, 1.0]
    coef[2] = -(3 + self._dist_to_opt**2 * self._h_min**2 / 2 / self._grad_var)
    roots = np.roots(coef)
    root = roots[np.logical_and(np.logical_and(np.real(roots) > 0.0, 
      np.real(roots) < 1.0), np.imag(roots) < 1e-5) ]
    assert root.size == 1
    dr = self._h_max / self._h_min
    self._mu_t = max(np.real(root)[0]**2, ( (np.sqrt(dr) - 1) / (np.sqrt(dr) + 1) )**2 )
    return