1. David Evans http://www.cs.virginia.edu/evans
Class 1:
Introduction
CS200: Computer Science
University of Virginia
Computer Science
David Evans

2. Menu What Is Computer Science? Why Computer Science is Not Engineering
First Main Theme: Recursive Definitions
Course Expectations
15 January 2003
CS 200 Spring 2003

3. What is Computer Science?
15 January 2003
CS 200 Spring 2003

4. Let AB and CD be the two given numbers not relatively prime
Let AB and CD be the two given numbers not relatively prime. It is required to find the greatest common measure of AB and CD.
If now CD measures AB, since it also measures itself, then CD is a common measure of CD and AB. And it is manifest that it is also the greatest, for no greater number than CD measures CD.
Euclid’s Elements, Book VII, Proposition 2 (300BC)
15 January 2003
CS 200 Spring 2003

5. The note on the inflected line is only difficult to you, because it is so easy. There is in fact nothing in it, but you think there must be some grand mystery hidden under that word inflected!
Whenever from any point without a given line, you draw a long to any point in the given line, you have inflected a line upon a given line.
Ada Byron (age 19), letter to Annabella Acheson (explaining Euclid), 1834
15 January 2003
CS 200 Spring 2003

6. By the word operation, we mean any process which alters the mutual relation of two or more things, be this relation of what kind it may. This is the most general definition, and would include all subjects in the universe... Supposing, for instance, that the fundamental relations of pitched sounds in the science of harmony and of musical composition were susceptible of such expression and adaptations, the engine might compose elaborate and scientific pieces of music of any degree of complexity or extent.
Ada Byron, 1843
15 January 2003
CS 200 Spring 2003

7. What is the difference between Euclid and Ada?
“It depends on what your definition of ‘is’ is.”
Bill Gates (at Microsoft’s anti- trust trial)
15 January 2003
CS 200 Spring 2003

8. Geometry vs. Computer Science
Geometry (mathematics) is about declarative knowledge: “what is”
If now CD measures AB, since it also measures itself, then CD is a common measure of CD and AB
Computer Science is about imperative knowledge: “how to”
Computer Science has nothing to do with beige (or translucent blue) boxes called “computers” and is not a science.
15 January 2003
CS 200 Spring 2003

9. Computer Science “How to” knowledge:
Ways of describing imperative processes (computations)
Ways of reasoning about (predicting) what imperative processes will do
Language
Logic
15 January 2003
CS 200 Spring 2003

10. Science, Engineering, Other?
15 January 2003
CS 200 Spring 2003

11. Science? Understanding Nature through Observation
About real things like bowling balls, black holes, antimatter, electrons, comets, etc.
Math and Computer Science are about fake things like numbers, graphs, functions, lists, etc.
Computer Science is a useful tool for doing real science, but not a real science
15 January 2003
CS 200 Spring 2003

12. Engineering?
“Engineering is design under constraint… Engineering is synthetic - it strives to create what can be, but it is constrained by nature, by cost, by concerns of safety, reliability, environmental impact, manufacturability, maintainability and many other such 'ilities.' ...”
William Wulf
15 January 2003
CS 200 Spring 2003

13. Apollo Guidance Computer, 1969
Why did they need to fit the guidance computer in the rocket?
1 Cubic Foot
15 January 2003
CS 200 Spring 2003

14. Measuring Computers 1 bit = smallest unit of information True or False
If we start with 2 possible choices, and get 1 bit, we can eliminate one of the choices
15 January 2003
CS 200 Spring 2003

15. How much power?
Apollo Computer: bits of changeable memory
Lab machines have 386 MB (RAM)
1 Megabyte = 1024 Kilobytes, 1 Kilobyte = 1024 Bytes, 1 Byte = 8 bits
386 MB = bits
> (* )
> (round (/ (* ) 30720))
105404
You have times more power than AGC
If Apollo Guidance Computer power is 1 inch, you have 1.6 miles!
15 January 2003
CS 200 Spring 2003

16. Computing Power 1969-2002 (in Apollo Control Computer Units)
Moore’s Law: computing power doubles every 18 months!

17. Constraints Computer Scientists Face
Not like those for engineers:
Cost, weight, physics, etc.
If 4 Million times what people had in 1969 isn’t enough for you, wait until 2006 and you will have 32 Million times…
More like those for Musicians and Poets:
Imagination and Creativity
Complexity of what we can understand
15 January 2003
CS 200 Spring 2003

18. So, what is computer science?
No: its about fake things like numbers, not about observing and understanding nature
Engineering
No: we don’t have to deal with engineering-type constraints
Liberal Art
15 January 2003
CS 200 Spring 2003

19. The Liberal Arts Quadrivium (4 roads) Trivium (3 roads) language
numbers
Trivium (3 roads)
Quadrivium (4 roads)
Grammar
Rhetoric
Logic
Arithmetic
Music
Geometry
Astronomy
15 January 2003
CS 200 Spring 2003

20. College of Arts and Sciences?
What is the real name of the College?
Web site: “College of Arts and Sciences”
Then what does “CLAS” stand for?
Col-Lege of Arts and Sciences?
Why does it have Government, Math and Foreign Languages Departments?
My theory:
The “Liberal” is Silent
15 January 2003
CS 200 Spring 2003

21. Liberal Arts Trivium Quadrivium
Grammar: study of meaning in written expression
Rhetoric: comprehension of verbal and written discourse
Logic: argumentative discourse for discovering truth
Arithmetic: understanding numbers
Geometry: quantification of space
Music: number in time
Astronomy: laws of the planets and stars
Yes, we need to understand
meaning to describe
computations
Trivium
Interfaces between
components, discourse
between programs and users
Logic for controlling
and reasoning about
computations
Yes (PS 6)
Yes (PS 1, 2, 3)
Quadrivium
Yes, its called GEB
for a reason!
Yes (we’ll read Neil DeGrasse Tyson’s essay)
15 January 2003
CS 200 Spring 2003

22. Bold (Possibly Untrue) Claim
This course is the most consistent with the original intent of a Liberal Arts education of any course offered at UVA this semester!
15 January 2003
CS 200 Spring 2003

23. First Main Theme: Recursive Definitions
15 January 2003
CS 200 Spring 2003

24. What is the longest word in the English language?
15 January 2003
CS 200 Spring 2003

25. floccipoccinihilipilification the act of rendering useless
According to Guinness
floccipoccinihilipilification
the act of rendering useless
15 January 2003
CS 200 Spring 2003

26. antifloccipoccinihilipilification
Making Longer Words
antifloccipoccinihilipilification
the act of rendering not useless
antiantifloccipoccinihilipilification the act of rendering useless
15 January 2003
CS 200 Spring 2003

27. Language is Recursive
No matter what word you think is the longest word, I can always make up a longer one!
word ::= anti-word
If you have a word, you can always make up a new word by adding anti in front. Since the result is a word, you can make a longer new word by adding anti- in front again.
15 January 2003
CS 200 Spring 2003

28. Recursive Definitions
We can define things in terms of themselves
Recursive definitions are different from circular definitions: they eventually end with something real
word ::= anti-word
word ::= floccipoccinihilipilification
15 January 2003
CS 200 Spring 2003

29. Recursive Definitions
Allow us to express infinitely many things starting with a few.
This is powerful!
We will see lots of examples in this course.
15 January 2003
CS 200 Spring 2003

30. Course Expectations
15 January 2003
CS 200 Spring 2003

31. What I Expect of You Everything on the Course Pledge
Read it and make sure you agree with it
Sign it and return it next class
Three most important attributes for succeeding in this course:
Open mind
Persistence
Willingness to spend time in Small Hall
15 January 2003
CS 200 Spring 2003

32. A Course for Everyone! CLAS, SEAS, etc.
First Years, Second Years, Third Years, Fourth Years
No background expected
…but challenging even for students with lots of previous CS courses
Computer Science (future-) majors
…but worthwhile even if you never take another CS course
Need to get course action
signed no later than Friday!
15 January 2003
CS 200 Spring 2003

33. What You Should Expect not The fourth (?) coolest class at UVa
Less cool than PHYE125, PHYE127, ENNC382
This course will be consistent with the original notion of a Liberal Arts education
This course will be as consistent as possible with Mr. Jefferson’s vision for the University
Scary live reptiles will
suddenly appear
in the classroom
You should expect these of all your classes!
not
15 January 2003
CS 200 Spring 2003

34. Like Drinking from a Firehose
It may hurt a little bit, and a lot of water will go by you, but you won’t go away thirsty!
15 January 2003
CS 200 Spring 2003

35. Persistence
Don’t expect to understand everything the first (or second or third) time you see it
Don’t worry if you don’t always understand everything completely
Take advantage of available help
But, make sure to understand the most important things well
Notes and Problem Sets should make it clear what this is
You will learn most from doing the Problem Sets
15 January 2003
CS 200 Spring 2003

36. Help Available Me: David Evans (Call me “Dave” or “Coach”)
Office Hours will be posted after surveys
Always available by , if I don’t reply in 24 hours, send again and complain
Assistant Coaches
Rachel Dada, Jacques Fournier,
Spencer Stockdale, Katie Winstanley
Web site:
Everything goes on the web
Your classmates (read the course pledge carefully!)
15 January 2003
CS 200 Spring 2003

37. Books
Abelson & Sussman, Structure and Interpretation of Computer Programs. (SICP)
Douglas Hofstadter, Gödel, Escher, Bach: an Eternal Golden Braid (GEB)
15 January 2003
CS 200 Spring 2003

38. Computer Science from Euclid and Ada to
Course Roadmap
Computer Science from Euclid and Ada to
Quantum Computing and the World Wide Web
Today
Intellectual
PS 1-6
PS 7
$$$
PS 8
15 January 2003
CS 200 Spring 2003

39. Charge Don’t floccipoccinihilipilificate PS1 is Due Wednesday
Before 5pm Thursday:
Registration survey (see course web site)
Before Friday:
Read and sign CS 200 Pledge
Read GEB p. 3-41
Anyone who can produce “MU”, gets an automatic A+ in the course
PS1 is Due Wednesday
Take advantage of the lab hours (listed on the PS handout)
Don’t floccipoccinihilipilificate
15 January 2003
CS 200 Spring 2003

40. Thanks!
CS Department: Jim Cohoon, Ginny Hilton, Anita Jones, John Knight, Worthy Martin, Chris Milner, Brenda Perkins, Gabe Robins, Jack Stankovic
Teaching Resource Center: Marva Barnett, Freda Fretwell
UTF Fellows: Phoebe Crisman, John Lach, Debra Lyon, Emily Scida, Brian Smith, David Waldner; UTF Mentor: Judith Shatin
2002 Assistant Coaches: Jon Erdman, Dante Guanlao, Stephen Liang, Portman Wills
2003 Assistant Coaches: Rachel Dada, Jacques Fournier, Spencer Stockdale, Katie Winstanley
2002 CS200 students, 2001 CS655 students
6.001 teachers: Gerry Sussman, Bob Berwick
6.001 discussions: Anna Chefter, Radhika Nagpal
15 January 2003
CS 200 Spring 2003