code: def output_AR1(results):
      """
      Compute the usual AR(1) parameter on
      the residuals from a regression.
      """
      resid = results.resid
      rho = np.add.reduce(
          resid[0:-1] * resid[1:] / np.add.reduce(resid[1:-1] ** 2)
      )
      return rho
  
file_path: nipy/nipy/modalities/fmri/fmristat/outputters.py
imports: import numpy
label_desc: Use image node_id 4 for calling a global function with example usage: output_AR1(results) and returns: rho