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Welcome to CS154

Welcome to CS154. Why Study Automata? What the Course is About Administrivia. Why Study Automata?. A survey of Stanford grads 5 years out asked which of their courses did they use in their job. Basics like CS106 took the top spots, of course.

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Welcome to CS154

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  1. Welcome to CS154 Why Study Automata? What the Course is About Administrivia

  2. Why Study Automata? • A survey of Stanford grads 5 years out asked which of their courses did they use in their job. • Basics like CS106 took the top spots, of course. • But among optional courses, CS154 stood remarkably high. • 3X the score for AI, for example.

  3. How Could That Be? • Regular expressions are used in many systems. • E.g., UNIX a.*b. • E.g., DTD’s describe XML tags with a RE format like person (name, addr, child*). • Finite automata model protocols, electronic circuits. • Theory is used in model-checking.

  4. How? – (2) • Context-free grammars are used to describe the syntax of essentially every programming language. • Not to forget their important role in describing natural languages. • And DTD’s taken as a whole, are really CFG’s.

  5. How? – (3) • When developing solutions to real problems, we often confront the limitations of what software can do. • Undecidable things – no program whatever can do it. • Intractable things – there are programs, but no fast programs. • CS154 gives you the tools.

  6. Other Good Stuff in CS154 • We’ll learn how to deal formally with discrete systems. • Proofs: You never really prove a program correct, but you need to be thinking of why a tricky technique really works. • We’ll gain experience with abstract models and constructions. • Models layered software architectures.

  7. Course Outline • Regular Languages and their descriptors: • Finite automata, nondeterministic finite automata, regular expressions. • Algorithms to decide questions about regular languages, e.g., is it empty? • Closure properties of regular languages.

  8. Course Outline – (2) • Context-free languages and their descriptors: • Context-free grammars, pushdown automata. • Decision and closure properties.

  9. Course Outline – (3) • Recursive and recursively enumerable languages. • Turing machines, decidability of problems. • The limit of what can be computed. • Intractable problems. • Problems that (appear to) require exponential time. • NP-completeness and beyond.

  10. CS154N • If you are taking CS154N, you should start coming to class when we enter the Turing-machine material.

  11. Meet the TA’s • Shrey Gupta • Rohan Jain • Jia Li

  12. Course Requirements • Two kinds of homework: • Gradiance homework (automated, straightforward, 20%). • Challenge problems (conventional written work, harder, 20%). • Two exams: • Midterm (20%). • Final (Monday June 7, 7-10PM, 40%).

  13. Text • Hopcroft, Motwani, Ullman, Automata Theory, Languages, and Computation 3rd Edition. • Course covers essentially the entire book.

  14. Gradiance Registration • The “class token” for this edition of CS154 is 1DC79FE7. • Register it at www.gradiance.com/pearson • Texts come with free access cards. • Go to www.aw-bc.com/gradiance to purchase or register (link at upper left).

  15. Comments About Gradiance Homework • The intent is that everyone will get 100% on all homeworks. • You are allowed to try as many times as you like. • Only the last try counts. • Don’t be afraid to guess and try again. • You’ll get some advice if you make a mistake.

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