[Test-driven] Implementing label_semantic_role with new API

[sidgoyal78]

I have found 2 issues:

• In this chapter, we need to be able to read the embedding parameters. However, with the new high level API, we can't modify the train_loop to read the params. Hence, this current implementation doesn't work.

More precisely, if we look at the earlier implementation: https://github.com/PaddlePaddle/Paddle/blob/develop/python/paddle/fluid/tests/book/test_label_semantic_roles.py#L200-L204

• There is a problem with the learning rate layer inside optimizer. I get the error:

 File "/usr/local/lib/python2.7/dist-packages/paddle/fluid/optimizer.py", line 73, in _create_global_learning_rate
    "learning rate variable is create outside optimizer,"
TypeError: learning rate variable is create outside optimizer,can not create new learning rate variable for new program

For reference, see original implementation: https://github.com/PaddlePaddle/Paddle/blob/develop/python/paddle/fluid/tests/book/test_label_semantic_roles.py#L173-L178

Potential fixes (which work)

• Issue 1: We can make the embedding layer trainable.
• Issue 2: We can get around the optimizer problem by having a straight-forward optimizer, which is done here.

[jetfuel]

@sidgoyal78 By the way, You will need to create a Makefile for this test. You can simply copy the Makefile from the other folder. Also we will need to add subdirectory in the parent Makefile like this
add_subdirectory(label_semantic_roles). Otherwise we will not run the test.

[sidgoyal78]

Yes, @jetfuel. I will add it after resolving the aforementioned issues. As of now, we have it as a notest script.