code: def create_function_f_J(self):
          
          return ca.Function(
              'J',
              [self.t, self.x, self.y, self.m, self.p, self.c, self.ng, self.nu],
              [ca.jacobian(self.f_x_rhs, self.x)],
              ['t', 'x', 'y', 'm', 'p', 'c', 'ng', 'nu'], ['J'], self.func_opt)
docs: Jacobian for state integration