code: def ar2lhs(ar):
      """convert full (rhs) lagpolynomial into a reduced, left side lagpoly array
  
      this is mainly a reminder about the definition
      """
      return -ar[1:]
  
imports: import numpy
  from scipy import signal
  from statsmodels.tsa.tsatools import lagmat
label_desc: Use image node_id 7 for calling a global function with example usage: ar2lhs(ar) and returns: unknown