class_docstr: experimental class for Covariance of AR process
  classmethod? staticmethods?
class_docstr_tok: ["experimental","class","for","Covariance","of","AR","process","classmethod","?","staticmethods","?"]
code: def __init__(self, ar=None, ar_coefs=None, sigma=1.0):
      if ar is not None:
          self.ar = ar
          self.ar_coefs = -ar[1:]
          self.k_lags = len(ar)
      elif ar_coefs is not None:
          self.arcoefs = ar_coefs
          self.ar = np.hstack(([1], -ar_coefs))
          self.k_lags = len(self.ar)
  
file_path: statsmodels/statsmodels/sandbox/panel/correlation_structures.py
imports: import numpy
  from statsmodels.regression.linear_model import yule_walker
  from statsmodels.stats.moment_helpers import cov2corr
label_desc: Use image node_id 1 to create a new ARCovariance object  with example: obj = ARCovariance(ar, ar_coefs, sigma)