C5W3 Quiz - Sequence models & Attention mechanism

Ans: False

Ans: A、B、C

Ans：A

Ans: A

Ans: A

Ans: A、D

False

Ans： True

Ans: A

Ans: B

Ans: A

1. Consider using this encoder-decoder model for machine translation.

This model is a “conditional language model” in the sense that the encoder portion (shown in green) is modeling the probability of the input sentence xx.

Ans: True

2. In beam search, if you increase the beam width BB, which of the following would you expect to be true? Check all that apply.

Ans: Beam search will run more slowly.

          Beam search will use up more memory.

          Beam search will generally find better solutions (i.e. do a better job maximizing P(y \mid x)P(y∣x))

3. In machine translation, if we carry out beam search without using sentence normalization, the algorithm will tend to output overly short translations.

Ans: True

4. Suppose you are building a speech recognition system, which uses an RNN model to map from audio clip x to a text transcript y. Your algorithm uses beam search to try to find the value of y that maximizes P(y∣x).

On a dev set example, given an input audio clip, your algorithm outputs the transcript y^ = “I’m building an A Eye system in Silly con Valley.”, whereas a human gives a much superior transcript y* = “I’m building an AI system in Silicon Valley.”

According to your model,

P(y^|x) = 1.09*10^-7

P(y∗∣x) = 7.21∗10^−8

Would you expect increasing the beam width B to help correct this example?

Ans: No, because P(y∗∣x) ≤ P(y^∣x) indicates the error should be attributed to the RNN rather than to the search algorithm.

5. Continuing the example from Q4, suppose you work on your algorithm for a few more weeks, and now find that for the vast majority of examples on which your algorithm makes a mistake, P(y∗∣x) > P(y^∣x). This suggest you should focus your attention on improving the search algorithm.

Ans: True.

6. Consider the attention model for machine translation. Further, here is the formula for α<t,t′>. Which of the following statements about α<t,t′> are true? Check all that apply.

         We expect α<t,t′> to be generally larger for values of a<t′> that are highly relevant to the value the network should output for y^{<t>}. (Note the indices in the superscripts.)

         ∑tα<t,t′> = 1 (Note the summation is over tt.)

7. The network learns where to “pay attention” by learning the values e<t,t′>, which are computed using a small neural network:

We can't replace s^{<t-1>} with s^{<t>} as an input to this neural network. This is because s^{<t>} depends on α<t,t′> which in turn depends on e<t,t′>; so at the time we need to evalute this network, we haven’t computed s^{<t>} yet.

         True

8. Compared to the encoder-decoder model shown in Question 1 of this quiz (which does not use an attention mechanism), we expect the attention model to have the greatest advantage when:

         The input sequence length Tx is large.

9. Under the CTC model, identical repeated characters not separated by the “blank” character (_) are collapsed. Under the CTC model, what does the following string collapse to? __c_oo_o_kk___b_ooooo__oo__kkk

         coookkboooooookkk

10. In trigger word detection, x^{<t>) is:

         Features of the audio (such as spectrogram features) at time t.