code: def tstd_dlldy(y, df):
      """derivative of log pdf of standardized t with respect to y
  
          Parameters
          ----------
      y : array_like
          data points of random variable at which loglike is evaluated
      df : array_like
          degrees of freedom,shape parameters of log-likelihood function
          of t distribution
  
      Returns
      -------
      dlldy : ndarray
          derivative of loglikelihood wrt random variable y evaluated at the
          points given in y
  
  
      Notes
      -----
      parametrized for garch, standardized to variance=1
      """
      # (df+1)/2. / (1 + y**2/(df-2.)) * 2.*y/(df-2.)
      return -(df + 1) / (df - 2.0) / (1 + y**2 / (df - 2.0)) * y
  
file_path: statsmodels/statsmodels/sandbox/regression/tools.py
imports: import numpy
  from scipy import special
  from scipy.special import gammaln
label_desc: Use image node_id 10 for calling a global function with example usage: tstd_dlldy(y, df) and returns: unknown