Created by: yaweisun

实现该接口的文件如下： https://github.com/PaddlePaddle/models/blob/develop/dygraph/lac/sequence_labeling.py 运行的环境是aistudio高级版，paddlepaddle 1.7.1, python 3.7 我调用的代码如下：

linear_chain_crf = Linear_chain_crf(
        param_attr=fluid.ParamAttr(
            name='linear_chain_crfw', learning_rate=LR),
        size=num_labels)
crf_cost = linear_chain_crf(emission, label=label, length=MAX_SEQLEN)

emission.shape和label.shape均为[16, 400, 5]。其中16是batch_size，400是序列最大长度，5是序列标注的类别数量。 执行之后报错，没有找到该接口对输入参数的具体要求，因而想咨询一下这是出现这个问题的原因。报错信息如下：

> ---------------------------------------EnforceNotMet                             Traceback (most recent call last)<ipython-input-36-85157a21fed9> in <module>
> ----> 1 linear_chain_crf(emission, label=label, length=128)
> /opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/dygraph/layers.py in __call__(self, *inputs, **kwargs)
>     302             self._built = True
>     303 
> --> 304         outputs = self.forward(*inputs, **kwargs)
>     305         return outputs
>     306 
> ~/ernie/sequence_labeling.py in forward(self, input, label, length)
>     177                         },
>     178                         attrs={
> --> 179                             "is_test": self._is_test,
>     180                         })
>     181         return log_likelihood
> /opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/dygraph/layer_object_helper.py in append_op(self, type, inputs, outputs, attrs, stop_gradient)
>      50             outputs=outputs,
>      51             attrs=attrs,
> ---> 52             stop_gradient=stop_gradient)
>      53 
>      54     def _multiple_input(self, inputs_in):
> /opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/framework.py in append_op(self, *args, **kwargs)
>    2514                                        kwargs.get("outputs", {}), attrs
>    2515                                        if attrs else {},
> -> 2516                                        kwargs.get("stop_gradient", False))
>    2517         else:
>    2518             op_desc = self.desc.append_op()
> /opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/dygraph/tracer.py in trace_op(self, type, inputs, outputs, attrs, stop_gradient)
>      37         self.trace(type, inputs, outputs, attrs,
>      38                    framework._current_expected_place(), self._train_mode and
> ---> 39                    not stop_gradient)
>      40 
>      41     def train_mode(self):
> EnforceNotMet: 
> 
> --------------------------------------------
> C++ Call Stacks (More useful to developers):
> --------------------------------------------
> 0   std::string paddle::platform::GetTraceBackString<std::string>(std::string&&, char const*, int)
> 1   paddle::platform::EnforceNotMet::EnforceNotMet(paddle::platform::ErrorSummary const&, char const*, int)
> 
> ----------------------
> Error Message Summary:
> ----------------------
> Error: Python object is not type of St10shared_ptrIN6paddle10imperative7VarBaseEE at (/paddle/paddle/fluid/pybind/imperative.cc:158)