code: def get_vert_connectivity(mesh_v, mesh_f):
      
  
      vpv = sp.csc_matrix((len(mesh_v),len(mesh_v)))
  
      # for each column in the faces...
      for i in range(3):
          IS = mesh_f[:,i]
          JS = mesh_f[:,(i+1)%3]
          data = np.ones(len(IS))
          ij = np.vstack((row(IS.flatten()), row(JS.flatten())))
          mtx = sp.csc_matrix((data, ij), shape=vpv.shape)
          vpv = vpv + mtx + mtx.T
  
      return vpv
docs: Returns a sparse matrix (of size #verts x #verts) where each nonzero
      element indicates a neighborhood relation. For example, if there is a
      nonzero element in position (15,12), that means vertex 15 is connected
      by an edge to vertex 12.