code: def get_jtimes_callback(self):
          
          jtimes = self.get_jtimes()
          if jtimes is False:
              return None
          v, jtimes_exprs = jtimes
          return _Callback(self.indep, tuple(self.dep) + tuple(v), self.params,
                           jtimes_exprs, Lambdify=self.be.Lambdify)
docs: Generate a callback fro evaluating the jacobian-vector product.