code: def stepped_1d(arr_1d):
      # Make a version of `arr_1d` which is not contiguous
      return np.vstack((arr_1d, arr_1d)).ravel(order="F")[::2]
  
imports: import numpy
  from dipy.data import default_sphere
  from dipy.tracking.propspeed import ndarray_offset, eudx_both_directions
  from numpy.testing import assert_equal, assert_raises
label_desc: Use image node_id 1 for calling a global function with example usage: stepped_1d(arr_1d) and returns: np