code: def example_formula():
      time_vector = make_recarray(FUNC_LIST.volume_start_times, "t")
      t = Term("t")
      con_defs = {"c": t, "c2": t + t**2}
      # Formula - with an intercept
      f = Formula([t, t**2, t**3, 1])
      # Design matrix and contrasts
      desmtx, cmatrices = f.design(time_vector, contrasts=con_defs)
      return f, desmtx, cmatrices
  
file_path: nipy/nipy/modalities/fmri/fmristat/tests/test_model.py
imports: import numpy
  import pytest
  from numpy.testing import assert_array_almost_equal, assert_array_equal
  from nipy.algorithms.statistics.formula.formulae import Formula, Term, make_recarray
  from nipy.algorithms.statistics.models.regression import OLSModel, ar_bias_correct
  from nipy.core.image.image import rollimg
  from nipy.io.api import load_image
  from nipy.testing import anatfile, funcfile
  from ...api import FmriImageList
  from ..None import model
  from ..model import ModelOutputImage, estimateAR
label_desc: Use image node_id 2 for calling a global function with example usage: example_formula() and returns: f,  desmtx,  cmatrices