code: def intersection(a, b, M):
      count = 0
      a_idx = M.indptr[a]
      b_idx = M.indptr[b]
  
      while (a_idx < M.indptr[a + 1]) and (b_idx < M.indptr[b + 1]):
          a_vertex = M.indices[a_idx]
          b_vertex = M.indices[b_idx]
  
          if a_vertex == b_vertex:
              count += 1
              a_idx += 1
              b_idx += 1
          elif a_vertex < b_vertex:
              a_idx += 1
          else:
              b_idx += 1
  
      return count
  
imports: import gc
  import pytest
  import numpy
  import scipy
  import cudf
  import cugraph
  from cugraph.testing import utils, UNDIRECTED_DATASETS
  from cudf.testing import assert_series_equal
  from cudf.testing.testing import assert_frame_equal
label_desc: Use image node_id 4 for calling a global function with example usage: intersection(a, b, M) and returns: count