def sanity_check_fb(self,forward,backward):
     return sanity_check_forward_backward(forward,backward)
 def forward_backward(self,seq):
     node_potentials,edge_potentials = self.build_potentials(seq)
     forward,backward = forward_backward(node_potentials,edge_potentials)
     sanity_check_forward_backward(forward,backward)
     return forward,backward