code: def _find_missing_index(ind, n):
      for k, a in enumerate(ind):
          if k != a:
              return k
  
      k += 1
      if k < n:
          return k
      else:
          return -1
  
imports: from __future__ import division, print_function, absolute_import
  import numpy
  from .base import spmatrix, _ufuncs_with_fixed_point_at_zero
  from .sputils import isscalarlike, validateaxis, matrix
label_desc: Use image node_id 1 for calling a global function with example usage: _find_missing_index(ind, n) and returns: k, unknown, k