code: def comb2(n):
      # the exact version is faster for k == 2: use it by default globally in
      # this module instead of the float approximate variant
      return comb(n, 2, exact=1)
  
imports: from __future__ import division
  from math import log
  import numpy
  from scipy.misc import comb
  from scipy import sparse
  from .expected_mutual_info_fast import expected_mutual_information
  from ...utils.fixes import bincount
  from ...utils.validation import check_array
label_desc: Use image node_id 1 for calling a global function with example usage: comb2(n) and returns: comb