1. David Evans http://www.cs.virginia.edu/~evans
Lecture 1: Introduction
Background
just got here last week
finished degree at MIT week before
Philosophy of advising students
don’t come to grad school to implement someone else’s idea
can get paid more to do that in industry
learn to be a researcher
important part of that is deciding what problems and ideas are worth spending time on
grad students should have their own project
looking for students who can come up with their own ideas for research
will take good students interested in things I’m interested in – systems, programming languages & compilers, security
rest of talk – give you a flavor of the kinds of things I am interested in
meant to give you ideas (hopefully even inspiration!) but not meant to suggest what you should work on
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 Mechanics
Pictures
16 January 2002
CS 200 Spring 2002

3. What is Computer Science?
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CS 200 Spring 2002

4. Euclid’s Elements, Book VII, Proposition 2 (300BC)
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. But, if CD does not measure AB, then, when the less of the numbers AB and CD being continually subtracted from the greater, some number is left which measures the one before it.
Euclid’s Elements, Book VII, Proposition 2 (300BC)
16 January 2002
CS 200 Spring 2002

5. Ada, Countess of Lovelace, around 1830
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. Again, it might act upon other things besides number, were objects found whose mutual fundamental relations could be expressed by those of the abstract science of operations, and which should be also susceptible of adaptations to the action of the operating notation and mechanism of the engine... 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, Countess of Lovelace, around 1830
16 January 2002
CS 200 Spring 2002

6. 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)
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CS 200 Spring 2002

7. 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.
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CS 200 Spring 2002

8. Computer Science “How to” knowledge:
Ways of describing imperative processes (computations)
Ways of reasoning about (predicting) what imperative processes will do
Language
Logic
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CS 200 Spring 2002

9. Science, Engineering, Other?
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CS 200 Spring 2002

10. 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
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CS 200 Spring 2002

11. 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
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CS 200 Spring 2002

12. Apollo Guidance Computer, 1969
Why did they need to fit the guidance computer in the rocket?
1 Cubic Foot
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CS 200 Spring 2002

13. 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
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CS 200 Spring 2002

14. How much power?
Apollo Guidance Computer: bits of changeable memory (stored in magnetic core)
Lab machines have 386 MB (RAM)
1 Byte = 8 bits
1 Kilobyte = 1024 Bytes
1 Megabyte = 1024 Kilobytes
386 MB = bits
> (* )
You have times more power than Apollo
> (round (/ (* ) 30720))
105404
If Apollo Guidance Computer power is 1 in, you have 1.6 miles!
16 January 2002
CS 200 Spring 2002

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

16. 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
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CS 200 Spring 2002

17. 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
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CS 200 Spring 2002

18. The Liberal Arts Quadrivium (4 roads) Trivium (3 roads) language
numbers
Trivium (3 roads)
Quadrivium (4 roads)
Grammar
Rhetoric
Logic
Arithmetic
Music
Geometry
Astronomy
16 January 2002
CS 200 Spring 2002

19. 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!
No, but astronomy uses CS a lot.
See corrected version in
Lecture 13!
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CS 200 Spring 2002

20. 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!
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CS 200 Spring 2002

21. First Main Theme
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CS 200 Spring 2002

22. Question What is the longest word in the English language?
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CS 200 Spring 2002

23. floccipoccinihilipilification the act of rendering useless
Longest word?
floccipoccinihilipilification
the act of rendering useless
16 January 2002
CS 200 Spring 2002

24. antifloccipoccinihilipilification
Making Longer Words
antifloccipoccinihilipilification
the act of not rendering useless
antifloccipoccinihilipilificationator
one who does the act of not rendering useless
16 January 2002
CS 200 Spring 2002

25. 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.
16 January 2002
CS 200 Spring 2002

26. 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
16 January 2002
CS 200 Spring 2002

27. 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.
16 January 2002
CS 200 Spring 2002

28. Course Philosophy and Mechanics
16 January 2002
CS 200 Spring 2002

29. Staff Coach: David Evans Assistant Coaches Joined UVA in Nov 1999
Call me “Dave” or “Coach”
Research areas: security, programming swarms
Assistant Coaches
Aaron (“Spiff”) Crickenberger
Jon Erdman
Dante Guanlao
Stephen Liang
16 January 2002
CS 200 Spring 2002

30. CS200 Experiment First time offered
Need to prove that CLAS students can do real Computer Science
First time offered
I will probably make lots of mistakes
But…you get to take it in a small class
16 January 2002
CS 200 Spring 2002

31. 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!
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CS 200 Spring 2002

32. 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
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
16 January 2002
CS 200 Spring 2002

33. Help Available Me TAs Web site: http://www.cs.virginia.edu/cs200
Office Hours: Wednesdays 2:30-3:30pm
Always available by , if I don’t reply in 24 hours, send again and complain
Lunch
TAs
Will post staffed lab hours
Web site:
Everything goes on the web
But mainly: your classmates
16 January 2002
CS 200 Spring 2002

34. Honor Code Classroom Pledge is Horrible!
The whole point of being at a University is so you can:
Learn from your classmates
Learn better by teaching your classmates
Sign and return the CS200 Pledge on Friday
16 January 2002
CS 200 Spring 2002

35. Don’t floccipoccinihilipilificate
Charge
Before 5pm Thursday:
registration survey
Need these to assign PS1 teams
Before Friday:
Read and sign CS 200 Pledge
Read GEB p. 3-41
Try to produce “MU”, anyone who does gets an automatic A+ in the course
Don’t floccipoccinihilipilificate
Remember to take pictures!
16 January 2002
CS 200 Spring 2002