CMSC 150INTRODUCTION

TOCOMPUTING

CS 150: Mon 9 Jan 2012

About Me

Dr. Lewis Barnett Office: 212A Jepson Hall Office Hours: Most anytime, but

especiallyMT 2:30 - 3:30 pm; WR 10:30 - 11:30 am;

lbarnett@richmond.edu http://www.mathcs.richmond.edu/~lbarnett/

First: Meet Doug

He Decides Network Connections

Connections Doug Can Choose

Hours to Install Each Connection

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What Doug Wants…

A set of connections so that: a connection to each place (no place left

out) no loops sum of all installation times is minimum

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three loops here

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one loop here

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no loops here

Start With A Smaller Example

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Which connections should you include?5

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Start With A Smaller Example

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Which connections should you include? Likely the shorter ones…

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Start With A Smaller Example

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Which connections should you include? Likely the shorter ones Less likely the longer ones…

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Step by Step…

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Step by Step…

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Step by Step…

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Step by Step…

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Step by Step…

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Step by Step…

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loop!

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Step by Step…

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Step by Step…

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− each place connected− no loops− sum of times is minimum5

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Minimal vs. Not

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− each place connected− no loops− sum of times is minimum

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54 − each place connected

− no loops− sum of times is NOT minimum

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You Try It…

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Was This Your Result ?

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− each place is connected− no loops− sum of times is minimum: 28 hours

Doug is a Happy Fellow!

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Your Next Task

Break into pairs…

Write down the procedure you used: think in general terms

how do you start? how do you proceed from there? when do you finish?

Your Algorithm

You have just written down your first algorithm Kruskal’s algorithm for finding Minimum

Spanning Tree

1. Include path with min time (ties broken arbitrarily)

2. Include next shortest path if it does not introduce a loop

3. Repeat step 2 until each place has a path connected to it

Algorithms

Algorithm: Set of instructions for solving a problem known starting condition well-defined sequence of steps terminates

Computation: applying an algorithm to an input to obtain an output (solution)

Key: different algorithms can solve same problem Choose the “best” algorithm

Applications of MST

Network Design computer, electrical, cable, road, … e.g., want set of lines that connects all

offices with minimum total cost

Real-time face verification Particle interactions in fluid flows Ethernet bridging to avoid cycles in

network

About This Course

An introduction to the science of computing

You will learn: how to think algorithmically how to write your solutions in a program

(in Java) how to debug and test your solutions

Remember…

Computer science is not (just) programming

Computer scientists do much more than program

They develop algorithms to solve

problems using the computer (and programs) incorporating a variety of disciplines myriad applications and real-world

benefits…

Google’s Autonomous Vehicle

But We Have To Start Simple…

JavaProgra

m(Source)

Compiler

JavaProgra

m(Byte Code)

You write the source codein an IDE, e.g., BlueJ

But We Have To Start Simple…

JavaProgra

m(Source)

Compiler

JavaProgra

m(Byte Code)

The compiler is a program thatconverts source to binary; Included in BlueJ

But We Have To Start Simple…

JavaProgra

m(Source)

Compiler

JavaProgra

m(Byte Code)

Byte code version can be executed on computer

Let’s Write Our First Program !