HOMEWORK 2 (CS 2731 / ISSP 2230)

Assigned: October 4, 2013

Due: October 17 or 22, 2013 (midnight)

There are both written and programming parts to this homework. The written part will be turned in via courseweb to facilitate automatic grading.

1. Multiple Choice

2. Programming

2.1 HMM Decoding (Viterbi)

• Implement the Viterbi algorithm (Fig. 5.17 on page 147 in Jurafsky and Martin).
  • Demonstrate the correctness of your implementation by running it with the HMM in Figure 6.3 on page 178 to compute the most likely weather sequence for the following observation sequence: 331122313
  • We will also test your implementation on another blind test observation sequence.

2.2 Parsing (Earley)

• Implement a basic version of the Earley algorithm (Fig 13.13 on page 444 in Jurafsky and Martin).
  • Demonstrate the correctness of your implementation by parsing "Book that flight" using the L1 grammar from the textbook (Fig. 13.1 on page 428).
  • We will also test your implementation using L1 to parse some other blind test sentences.

• Augmentation 1: Modify your basic algorithm so that parse trees are retrieved from the chart. To do this, modify the psudocode for COMPLETER as described on page 448.

• Augmentation 2: Modify your basic algorithm so that it makes better use of bottom-up information to reduce the number of useless predictions. Parse an example with and without Augmentation 2 that illustrates the advantage of your approach (and explain why!).