code: def wang_ryzin_reg(h, Xi, x):
      """
      A version for the Wang-Ryzin kernel for nonparametric regression.
  
      Suggested by Li and Racine in [1] ch.4
      """
      return h ** abs(Xi - x)
  
file_path: statsmodels/statsmodels/nonparametric/kernels.py
imports: import numpy
  from scipy.special import erf
label_desc: Use image node_id 13 for calling a global function with example usage: wang_ryzin_reg(h, Xi, x) and returns: unknown