CS146 Overview

Problem Solving by Computing

Human Level

Virtual Machine

Actual Computer

Virtual Machine Level L0

Languages, Levels, Virtual Machines

A multilevel machine

Languages, Levels, Virtual Machines

Problem Solving by Computing

Human Level

(Algorithms)

Machine Level Ln

(JAVA )

What is an Algorithm?

An algorithm is a well-defined computational procedure that takes some value or set of values, as input and produce some value or set of values as output.

A “tool” for solving a well-specified computational problem

Sorting Problem

Input: A sequence of numbers (a1, a2, . . .)

Output: A reording (a’1, a’2, . . .) of the input such that a’1 a’2 . . .

Simple Sorting Algorithms

1. Insertion Sort

2. Merge Sort

3. Quick Sort

Simple Sorting Algorithms

1. Insertion Sort

2. Merge Sort

3. Quick Sort

Insertion Sort

j 2 to length[A]

Do A[j] key

insert A[j] into A[1, 2, … j-1]

i j-1

While i > 0 and A[I]> key

Do A[i+1] A[i]

i i-1

A[i+1] key

5 2 4 6 1 3

j=2

2

i=j-1=1 Key=2

A[1]>key 1>0

5 2

Latent Semantic Index

Project:

Compute the LSI (Latent Semantic Index) of a set of web pages/text files, such as Google’s return.

Sort a web page or a text file (XML or Text) in alphabetical order

Latent Semantic Index

1. Sort a web page or a text file (XML or Text)

2. Create an Inverted file

Attached to each words a list of locations that this word has appeared

Latent Semantic Index

1. Applications

2. Use LSI, we can cluster (classify) the return of Google’s search into meaningful group