code: def test_fss_varying_radius():
      # For each "f1" streamlines search all in radius of "f2"
      fss = FastStreamlineSearch(
          f1,
          max_radius=10.0,
          nb_mpts=5,
          bin_size=20.0,
          resampling=25,
          bidirectional=True,
      )
      rs_6 = fss.radius_search(f2, radius=6.0, use_negative=True)
      rs_4 = fss.radius_search(f2, radius=4.0, use_negative=True)
      rs_2 = fss.radius_search(f2, radius=2.0, use_negative=True)
  
      # smaller radius should be a subset or equal of a bigger radius
      assert_greater_equal(rs_6.nnz, rs_4.nnz)
      assert_true(np.all(np.in1d(rs_4.row, rs_6.row)))
      assert_true(np.all(np.in1d(rs_4.col, rs_6.col)))
  
      assert_greater_equal(rs_4.nnz, rs_2.nnz)
      assert_true(np.all(np.in1d(rs_2.row, rs_4.row)))
      assert_true(np.all(np.in1d(rs_2.col, rs_4.col)))
  
file_path: dipy/dipy/segment/tests/test_fss.py
imports: import numpy
  from dipy.data import get_fnames
  from dipy.io.streamline import load_tractogram
  from dipy.segment.fss import FastStreamlineSearch, nearest_from_matrix_row, nearest_from_matrix_col
  from dipy.segment.metric import mean_euclidean_distance
  from dipy.testing import assert_arrays_equal, assert_greater, assert_greater_equal, assert_true
  from numpy.testing import assert_almost_equal, assert_raises
label_desc: Use image node_id 3 for calling a global function with example usage: test_fss_varying_radius() without return types