Lecture 1: Introduction - CS Rutgers

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Lecture 1: Introduction CS105: Great Insights in Computer Science Michael L. Littman, Fall 2006

Welcome! • CS105, taught last semester as “Topics in Computer Science”, but is now officially “Great Insights in Computer Science”. • Several innovations this semester: - Using Rutgers’ online course support - iClickers for in-class interaction - Programs for out-of-class interaction

Survey Region 1

Region 2

100

• Do you have a clicker? 75 A. no

50

B. yes

25 0 2004

2005

2006

2007

About Me • 1996: PhD, “Algorithms for Sequential Decision Making” (AI). • 1996-1999: Professor at Duke. • 2000-2002: (Back) to NJ, AT&T Labs Research.

• 2002–: Rutgers: heading “Rutgers Laboratory for RealLife Reinforcement Learning” (RL3).

My Course Goals • Cool facts, cool ideas. Ideas are “how to” facts. Shoot for one or two per lecture. • People (my parents, say), don’t understand how I have a PhD in CS and can’t help them when their Windows box crashes. • If it’s not about XP, what else is there? - That’s what I want to tell you...

Introduction to CS101s • Target audience: Undergrads, as a first (possibly only) computer-science course. • Seminar in Computers and Society: What impact have computers had on the world? • Introduction to Computer Science: How do I learn to create my own software? • Introduction to Computers and Their Application: What do I need to know about computing technology?

Course Goals: Questions • What is Computer Science? • Why is it fun/interesting? • How is it different from software engineering? • What are the insights that make computer science its own academic discipline?

Textbook • Not too daunting or detailed.

• Enjoyable to read; not really a textbook at all.

• Inspiring and informative.

• I will add meat to the wonderful skeleton he creates.

• Pattern on the Stone, the simple ideas that make computers work, Danny Hillis, Basic Books, 1998.

Clickers • Available at several bookstores. • Can keep them (most popular clicker at Rutgers) or sell them back. • We’ll use them for attendence, reading comprehension quizzes, straw polls.

• Hope to eventually add interactive demos, but software not yet ready.

http://www.iclicker.com/

Syllabus: Top-level View Organizing the material into three major sections: I. How does a computer work? II. What do we know about computation? III. What cool things are computers doing?

I. How Computers Work • Sequence of easy-to-understand layers. • Top: high-level programming languages express ideas in a computer-friendly form.

• Bottom: bits and logic gates, computer's work done by physical components.

• We'll go bottom up, conceptually creating a working computer in the process.

II. Computation • Computers compute. But, what is computation, and how powerful is it? • How do computer scientists see the world in terms of computational problems? • What’s an algorithm, why might one be preferred to another if they solve the same problem? • What problems can be solved and how fast?

III. Useful Applications We’ll survey how computing power is being harnessed.

• machine learning,

• robotics • genetic algorithms • data compression

pattern recognition

• computer graphics • AI search • language games

They Are Everywhere! • 1977: “There is no reason for any individual to have a computer in his home.”

• Today: Cell phone? PDA? Computers at home? Laptop? Video games? Digital camera?

Survey • How many computers are with you right now? Laptop, handheld game, cell phone, GPS device, PDA, mp3 player, ... A. 0 B. 1 C. 2 D. 3 E. 4 or more

Previously Unthinkable

Life After Death?

One-Word Summary • If I had to summarize the intellectual contribution of computer science in one word, it would be “reduction”. • Computer scientists solve problems by reducing them to simpler problems.

• We’ll see this same idea played out over and over again in different settings...

Levels of Complexity • Networking (OSI Layers): application, presentation, session, transport, network, data link, physical.

• Computing: application, high-level language, machine language, logic blocks, logic gates, physical.

• Vision (Marr): computational, algorithmic, implementation.

• Storage hierarchy: offline-storage, hard disk, RAM, cache, registers.

Today’s Idea • I will start with the textbook next time, introducing bits and some simple gates. • Please read the Preface and Chapter 1, Section 1. • But, I want to give you something to chew on to get those gears turning...

Your Choice • Babbage’s Difference Engine - Simple computation for sequences • How do UPC barcodes work? - Hierarchy of codes A. Difference Engine B. UPC barcodes

Charles Babbage: Facts • Charles Babbage lived in England in the 1800s. A polymath, he solved problems from Astronomy to Zoology. • Invented: cowcatcher, flat-rate postage, Operations Research, standard RR gauge.

• Held Newton’s chair at Cambridge, but spent his last years railing against organ grinders. • His design for the analytical engine presaged much of the design of modern digital computers.

The Difference Engine • Originally a “computer” was a job description of a person who created numerical tables. Useful, if tedious. • Babbage had a scheme to automate table creation using “finite differences”. • 25,000 parts, 15 tons, 8 feet high, never built! • His redesigned Difference Engine No. 2 was built in 1990 and actually worked!

Difference Engine: Ideas Let’s play a game: • 0,1,2,3,4,__? • 3,5,7,9,11,__? • 1,4,9,16,25,__? • 1,3,6,10,15,__?

Generating the Evens 2 4 6 8 10 12 2 2 2 2 2 Instructions: Start with 2. To get the next one, add 2 to the previous one.

1. 2.

Generating Squares 1 4 9 16 25 36 3 5 7 9 11 2 2 2 2 Instructions: Start with 1. Start the increment with 3. To get the next one, add the increment. To get the next increment, add 2 to the previous one.

1. 2. 3. 4.

Naming The Sequences 2 4 6 8 10 12 2 2 2 2 2 The Evens

Sequence: 1,4, 9, 16, 25, 36, ...

1 4 9 16 25 36 11 Program: 3 5 7 9 2 2 2 2 1,3,2 The Squares

Programming the “DE” • So, to produce the Evens, we enter “2 2” into the Difference Engine and turn the crank. • The Squares are “1 3 2”. • The Triangle numbers are “1 2 1”. • Try: - Odds?

- Count by 5s? - Cubes? • What do these do: - “4”? - “10 -1”? - “100 -19 2”? - “0 1 2 1”?

CS in a Microcosm? • Get a feel for programming: need to figure out how to say what you want to say in a way the machine understands. • Simple operation (repeated addition) used to build up more complex objects.

More Advanced Stuff • Each difference sequence corresponds to a polynomial and vice versa. Why? What is the relationship between the length of the difference sequence and the degree of the polynomial? • Can match any finitelength sequence. How long might the difference sequence need to be?

• You can start a sequence at any point by starting with the corresponding column. How can a sequence be moved backward automatically? • Download “Python” and play with it yourself! http://www.cs.rutgers.edu/~mlittman/ courses/cs442-06/python/

differences.py

Bar Codes • See http://en.wikipedia.org/wiki/Barcode . • Many different styles of barcodes. • Most common is UPC-A, in use in most North American retail stores. • I will describe the UPC encoding. • Many of the same ideas apply to other codes: checks, photostamps, IR remotes

Universal Product Codes • First scanned product, Wrigley’s gun (1974). • Method of identifying products at point of sale by 11-digit numbers. • Method of encoding digit sequences so they can be read quickly and easily by machine.

Reduction Idea • Each level uses an encoding to translate to the next level. - Patterns of ink. - Sequence of 95 zeros and ones. - Sequence of 12 digits. - Sequence of 11 digits. - Name of a retail product.

Product Name • Ponds Dry Skin Cream - 3.9 oz (110g) - Unilever Home and Personal Care USA • Name Badge Labels ( Size 2 3/16" x 3 3/8") - 100 Labels - Avery Dennison/Avery Division

11-Digit Number • Digit = {0,1,2,3,4,5,6,7,8,9} • Sequence of 11 digits • How many different items can they encode? A. 10,000,000,000 B. 100,000,000,000 C.

9,999,999,999

D. 19,999,999,999

Encode Name By 11 Digits • First 6 digits: Manufacturer - First digit, product category: . 0, 1, 6, 7, 8, or 9: most products . 2: store’s use, for variable-weight items . 3: drugs by National Drug Code number • Last 5 digits: Manufacturer-assigned ID

Examples • Labels: 0-72782-051440 - 0=general product - 72782= Avery - 051440=Avery’s code for this product • Ponds: 3-05210-04300 - 3=drug code - 05210= Unilever - 04300=National Drug Code for this product

12-Digit Number • The UPC folks decided to include another digit for error checking. Example: - 01660000070 Roses Lime Juice (12 oz) - 04660000070 Eckrich Franks, Jumbo (16 oz) - 05660000070 Reese PB/Choc Egg (34 g) - 08660000070 Bumble Bee Salmon (14.75 OZ) • Misread digit #2 and you turn sweet to sour.

Check Digit 1. Add the digits in the odd-numbered positions (first, third, fifth, etc.) together and multiply by three. 2. Add the digits in the even-numbered positions (second, fourth, sixth, etc.) to the result. 3. Subtract the result from the next-higher multiple of ten. The result is the check digit.

Code and Example def checkDigit(d1,d2,d3,d4,d5,d6,d7,d8,d9,d10,d11): step1 = (d1+d3+d5+d7+d9+d11)*3 step2 = step1+d2+d4+d6+d8+d10 01660000070 step3 = (-step2)%10 odd-digit sum: 0+6+0+0+0+0=6 return step3

even-digit sum: 1+6+0+0+7=14 odd*3+even = 6*3+14=32 subtract from mult of 10=40-32=8 • Lime juice: 01660000070!016600000708 • Franks:

04660000070!046600000705

• Choc Egg: 05660000070!056600000704 • Salmon:

08660000070!086600000701

all are two digits different now

Bits • We’ve gone from a product name to an 11-digit number to a 12-digit number. Next: bits. • abcdefghijkl!101abcdef01010 ghijkl ghijkl101 Digits encoded as 7-bit patterns, chosen to be: •as different as possible •start with 0, end with 1 •switch from 0 to 1 twice •no more than 4 of the same bit in a row

Last 6 digits have 0s and 1s reversed! 0: 0001101 5: 0110001 1: 0011001 6: 0101111 2: 0010011 7: 0111011 3: 0111101 8: 0110111 4: 0100011 9: 0001011

How Many Bits? • From our 12-digit number, how many bits (zeros and ones) long is the code now? A. 84 B. 95 C. 100 D. 23 E. 12

Finally, Ink! • Given the long pattern of bits, we write a 1 as a bar and a zero as a space. • Two 1s in a row become a double wide bar. • Two 0s in a row become a double wide space. • Never have more than 4 in a row. • Starts and ends with bars.

Example

.......

• Barcode for skin cream: • 3-05210-04300-8 (8 is the check digit) start: 101; 3: 0111101 05210: 0001101-0110001-0010011-0011001-0001101 middle: 01010 04300: 1110010-1011100-1000010-1110010-1110010 (rev) 8: 1001000 (rev); end: 101

• The digits underneath are for our benefit.

Close Up 10101111010001101011000100100110011001000110101010111001010111001000010111001011100101001000101

Summary • Product name turned to 11-digit code • 11-digit code extended to 12 digits by adding a check digit • 12 digits become a 95-bit sequence • 95 bits are drawn in ink 1=black,0=white Reverse the process to get the product!

Next Time • Get iClicker • Read Hillis: Preface and Chapter 1, up to and including “Boolean Logic”. • We’ll have a brief iClicker quiz on the material.

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Lecture 1: Introduction - CS Rutgers

Lecture 1: Introduction CS105: Great Insights in Computer Science Michael L. Littman, Fall 2006 Welcome! • CS105, taught last semester as “Topics in ...

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