Swapping the order of the inputs of layer.fc will cause error.

[xinghai-sun]

It's weird that an error occurs when we just swap the order of the input layers of layer.fc.

For example:

import paddle.v2 as paddle


def main():
    hidden_size = 128
    dict_size = 30000
    paddle.init(use_gpu=False, trainer_count=1)

    words = paddle.layer.data(
        name="words",
        type=paddle.data_type.integer_value_sequence(dict_size))
    next_words = paddle.layer.data(
        name='next_words',
        type=paddle.data_type.integer_value_sequence(dict_size))

    def recurrent_step(embedding):
        last_memory = paddle.layer.memory(name="memory", size=hidden_size)
        memory_update = paddle.layer.fc(
            name="memory", input=[last_memory, embedding], size=hidden_size)
        predict = paddle.layer.fc(
            input=[embedding, memory_update],
            size=dict_size,
            act=paddle.activation.Softmax())
        return predict

    predict_seq = paddle.layer.recurrent_group(
        step=recurrent_step,
        input=[paddle.layer.embedding(input=words, size=hidden_size)])
    cost = paddle.layer.classification_cost(
        input=predict_seq, label=next_words)

    parameters = paddle.parameters.create(cost)


if __name__ == '__main__':
    main()

This works OK. But if we swap the order of the fc layer's inputs, from

        predict = paddle.layer.fc(
            input=[embedding, memory_update],
            size=dict_size,
            act=paddle.activation.Softmax())

to

        predict = paddle.layer.fc(
            input=[memory_update, embedding],
            size=dict_size,
            act=paddle.activation.Softmax())

We will have the error:

Traceback (most recent call last):
  File "bug.py", line 39, in <module>
    main()
  File "bug.py", line 32, in main
    parameters = paddle.parameters.create(cost)
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/parameters.py", line 19, in create
    topology = Topology(layers)
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/topology.py", line 69, in __init__
    layers, extra_layers=extra_layers)
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/layer.py", line 96, in parse_network
    return __parse__(__real_func__)
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer_config_helpers/config_parser_utils.py", line 32, in parse_network_config
    config = config_parser.parse_config(network_conf, config_arg_str)
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer/config_parser.py", line 3597, in parse_config
    trainer_config()
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/layer.py", line 89, in __real_func__
    real_output = [each.to_proto(context=context) for each in output_layers]
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 109, in to_proto
    context=context)
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 112, in to_proto
    self.__parent_layers__[layer_name])
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 111, in <lambda>
    v1_layer = map(lambda x: x.to_proto(context=context),
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 112, in to_proto
    self.__parent_layers__[layer_name])
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 111, in <lambda>
    v1_layer = map(lambda x: x.to_proto(context=context),
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 112, in to_proto
    self.__parent_layers__[layer_name])
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 111, in <lambda>
    v1_layer = map(lambda x: x.to_proto(context=context),
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/config_base.py", line 116, in to_proto
    ret_val = self.to_proto_impl(**kwargs)
  File "/usr/local/lib/python2.7/site-packages/paddle/v2/layer.py", line 197, in to_proto_impl
    return conf_helps.memory(name=self.name, **args)
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer_config_helpers/default_decorators.py", line 53, in __wrapper__
    return func(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer_config_helpers/layers.py", line 2927, in memory
    memory_name=memory_name)
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer/config_parser.py", line 2337, in Memory
    agent_layer = AgentLayer(agent_name, size)
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer/config_parser.py", line 2243, in __init__
    name, 'agent', size, inputs=[], device=device)
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer/config_parser.py", line 1441, in __init__
    height = self.get_input_layer(0).height
  File "/usr/local/lib/python2.7/site-packages/paddle/trainer/config_parser.py", line 1447, in get_input_layer
    return g_layer_map[self.config.inputs[input_index].input_layer_name]
  File "/usr/local/lib/python2.7/site-packages/google/protobuf/internal/containers.py", line 204, in __getitem__
    return self._values[key]
IndexError: list index out of range

which is not expected.

Notice that this happens within a recurrent_group.

Version: docker.paddlepaddle.org/paddle:0.10.0rc3