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## David Evans cs.virginia/evans

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**Class 1:**Introduction David Evans http://www.cs.virginia.edu/evans CS200: Computer Science University of Virginia Computer Science**Menu**• What Is Computer Science? • Why Computer Science is Not Engineering • First Main Theme: Recursive Definitions • Course Expectations CS 200 Spring 2003**What is Computer Science?**CS 200 Spring 2003**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) CS 200 Spring 2003**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 CS 200 Spring 2003**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 CS 200 Spring 2003**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) CS 200 Spring 2003**Geometry vs. Computer Science**• Geometry (mathematics) is about declarative knowledge: “what is” If now CD measures AB, since it also measures itself, then CDis 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. CS 200 Spring 2003**Computer Science**“How to” knowledge: • Ways of describing imperative processes (computations) • Ways of reasoning about (predicting) what imperative processes will do Language Logic CS 200 Spring 2003**Science, Engineering, Other?**CS 200 Spring 2003**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 CS 200 Spring 2003**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 CS 200 Spring 2003**Apollo Guidance Computer, 1969**Why did they need to fit the guidance computer in the rocket? 1 Cubic Foot CS 200 Spring 2003**Measuring Computers**• 1 bit = smallest unit of information • True or False • 0 or 1 • If we start with 2 possible choices, and get 1 bit, we can eliminate one of the choices CS 200 Spring 2003**How much power?**• Apollo Computer: 30720 bits of changeable memory • Lab machines have 386 MB (RAM) • 1 Megabyte = 1024 Kilobytes, 1 Kilobyte = 1024 Bytes, 1 Byte = 8 bits • 386 MB = 3 238 002 688 bits > (* 386 1024 1024 8) 3238002688 > (round (/ (* 386 1024 1024 8) 30720)) 105404 You have 105 404 times more power than AGC If Apollo Guidance Computer power is 1 inch, you have 1.6 miles! CS 200 Spring 2003**Computing Power 1969-2002(in Apollo Control Computer Units)**Moore’s Law: computing power doubles every 18 months!**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 CS 200 Spring 2003**So, what is computer science?**• 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 CS 200 Spring 2003**The Liberal Arts**language numbers Quadrivium (4 roads) Trivium (3 roads) Grammar Rhetoric Logic Arithmetic Music Geometry Astronomy CS 200 Spring 2003**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 CS 200 Spring 2003**Liberal Arts**Yes, we need to understand meaning to describe computations • 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 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) CS 200 Spring 2003**This course is the most consistent with the original intent**of a Liberal Arts education of any course offered at UVA this semester! Bold (Possibly Untrue) Claim CS 200 Spring 2003**First Main Theme:Recursive Definitions**CS 200 Spring 2003**What is the longest word in the English language?**CS 200 Spring 2003**According to Guinness**floccipoccinihilipilification the act of rendering useless CS 200 Spring 2003**Making Longer Words**antifloccipoccinihilipilification the act of rendering not useless antiantifloccipoccinihilipilificationthe act of rendering useless CS 200 Spring 2003**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. CS 200 Spring 2003**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 CS 200 Spring 2003**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. CS 200 Spring 2003**Course Expectations**CS 200 Spring 2003**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 CS 200 Spring 2003**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! CS 200 Spring 2003**What You Should Expect**• 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 CS 200 Spring 2003**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! CS 200 Spring 2003**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 CS 200 Spring 2003**Help Available**• Me: David Evans (Call me “Dave” or “Coach”) • Office Hours will be posted after surveys • Always available by email, if I don’t reply in 24 hours, send again and complain • Assistant Coaches • Rachel Dada, Jacques Fournier, Spencer Stockdale, Katie Winstanley • Web site: http://www.cs.virginia.edu/cs200 • Everything goes on the web • Your classmates (read the course pledge carefully!) CS 200 Spring 2003**Books**Abelson & Sussman, Structure and Interpretation of Computer Programs. (SICP) Douglas Hofstadter, Gödel, Escher, Bach: an Eternal Golden Braid (GEB) CS 200 Spring 2003**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 CS 200 Spring 2003**Charge**• 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 CS 200 Spring 2003**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 • 2001-2 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 CS 200 Spring 2003