Assignment 2

UCR - CS 172 –Spring 2024

Instructions: Submit in Canvas by 5/18. This is individual assignment.

Exercise A

1. Compute the first 1 iteration of PageRank scores (d=0.7) of each node in the graph below. Show your work.

2. Write a program (e.g., in Java) to compute the final scores of the nodes and the number of iterations needed to converge, if we use convergence constant epsilon=0.001.

3. If we use personalized PageRank with nodes 1 and 2 in the base set, write the first iteration of the PageRank formulas.

Exercise B

Show how MapReduce can be used to efficiently solve the following problem:

Given a collection C of input documents, output all words with more than 8 characters that appear in more than 2 documents.

For example, if input documents are:

D1: hi there incredible

D2: hi incredible play application

D3: it is incredible

the output will be: "incredible"

Write pseudocode for map and reduce functions.

Full points will be given to efficient solutions.

Exercise C

Consider query Q that has a total of 6 relevant results in the collection, and a search engine that returns results:

r r x x r x x x r, where x is a relevant result and r is not relevant.

1. Compute Precision-at-4, Recall-at-4, F1-at-4, Average Precision, and DCG-at-4 (assuming relevant results have score 1 and non-relevant 0).

2. Mention an application where higher precision is more important than higher recall and one for the opposite.