code: def chirp_linear(t, f0, f1, t1):
      f = f0 + (f1 - f0) * t / t1
      return f
  
imports: import numpy
  from numpy.testing import assert_almost_equal, assert_equal, assert_, assert_allclose, assert_array_equal
  from pytest import raises
  import scipy.signal.waveforms
label_desc: Use image node_id 1 for calling a global function with example usage: chirp_linear(t, f0, f1, t1) and returns: f