code: def _switch_vertex(index1, index2, vertices):
      """When we mirror an edge (a, b). We can either create (a, b) and (a', b')
      OR (a, b') and (a', b). The angles of edges (a, b) and (a, b') are
      supplementary, so we choose the two new edges such that their angles are
      less than 90 degrees.
      """
      n = len(vertices)
      A = vertices[index1]
      B = vertices[index2]
      is_far = (A * B).sum(-1) < 0
      index2[is_far] = index2[is_far] + (n / 2.0)
      index2 %= n
  
imports: import numpy
  import warnings
  from scipy import optimize
  from dipy.core.geometry import cart2sphere, sphere2cart, vector_norm
  from dipy.core.onetime import auto_attr
  from dipy.reconst.recspeed import remove_similar_vertices
label_desc: Use image node_id 6 for calling a global function with example usage: _switch_vertex(index1, index2, vertices) without return types