code: def test_sofm_hexagon_grid(self):
      data = make_circle(max_samples=100)
      sofm = algorithms.SOFM(
          n_inputs=2,
          n_outputs=9,
          learning_radius=1,
          reduce_radius_after=4,
          features_grid=(3, 3),
          verbose=False,
          grid_type="hexagon",
      )
      sofm.train(data, epochs=10)
      grid = sofm.weight.reshape((2, 3, 3))
  
      center = grid[:, 1, 1]
      top_left = grid[:, 0, 0]
      top_right = grid[:, 0, 2]
  
      distance_top_left = np.linalg.norm(center - top_left)
      distance_top_right = np.linalg.norm(center - top_right)
  
      self.assertLess(distance_top_right, distance_top_left)
  
      bottom_left = grid[:, 2, 0]
      bottom_right = grid[:, 2, 2]
  
      distance_bottom_left = np.linalg.norm(center - bottom_left)
      distance_bottom_right = np.linalg.norm(center - bottom_right)
  
      self.assertLess(distance_bottom_right, distance_bottom_left)
  
imports: import math
  import numpy
  from neupy import algorithms
  from neupy.exceptions import WeightInitializationError
  from neupy.algorithms.competitive import sofm
  from neupy.algorithms.competitive.neighbours import gaussian_df
  from base import BaseTestCase
label_desc: Use image node_id 14 for calling the SOFMTestCase obj's underlying member method code with example usage: obj.test_sofm_hexagon_grid() without return types