Computational Complexity Theory, Fall 2008
CT08 / Lectures

August 27 2008
Introduction. The sequential Turing machine model. Time complexity. Simple lower bound using crossing sequences. Tape reduction. Efficient universal Turing machines. Time hierarchy theorem.

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August 29 2008
Space complexity. Simple lower bound using crossing sequences. Space hierarchy Theorem. Nondeterministic complexity. Relationships between space and time complexity. The reachability method. Savitch' Theorem.

Suggested reading materials:

  • Chapter 10 of Formal languages and their relation to automata by John E. Hopcroft Jeffrey D. Ullman.
  • Chapter 4 of Complexity Theory: A Modern Approach by Sanjeev Arora and Boaz Barak. (Skip parts about PSPACE)

September 3 2008
Logspace reductions. STCON is complete for NL. CVP is complete for P. The Immerman-Szelepcsenyi theorem. Nondeterministic space hierarchy theorem.

Suggested reading materials:

  • Chapter 4 of Complexity Theory: A Modern Approach by Sanjeev Arora and Boaz Barak. (Skip parts about PSPACE)

September 5 2008
Logspace uniform circuit characterization of P. Circuit SAT is complete for NP. Alternating Turing Machines. The Polynomial Time Hierarchy.

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September 10 2008
Oracle Turing Machines. Oracle definition of the Polynomial Time Hierarchy. Complete problems for PSPACE and levels of PH.

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September 12 2008
Time-space lower bounds for SAT. Collapse of PH. Karp-Lipton theorem. Meyer's Theorem. Relativization.

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September 17 2008
No lecture!

I recommend you instead watch the following video-lecture: Coding Theory: Survey of Recent Progress and Open Questions by Madhu Sudan.

We will use error correcting codes later in this course.

September 19 2008
No lecture!

I recommend you instead watch the following video-lecture: Discrete Mathematics: Expanders Graphs & Eigenvalues by Nati Linial.

We will use expander graphs later in this course.

September 24 2008
Parallel computation. PRAM's, ATM's and Boolean Circuits. NC and AC hierarchies. ADDITION is in AC0.

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September 26 2008
Threshold Circuits and TC0. TC0 is contained in NC1. MULTIPLICATION is in TC0. Introduction to the switching lemma and lower bounds for AC0.

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October 1 2008
Proof of the switching lemma and lower bounds for AC0.

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October 3 2008
The Razborov-Smolensky circuit bound. Barrington's Theorem.

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October 8 2008
Randomized Computation. Arithmetic Circuit Identity Testing. Classes BPP, RP, ZPP. Amplification. BPP is in P/poly.

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October 10 2008
BPP is in PH. Randomized logspace. Random walks and USTCON.

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November 5 2008
Recap of random walks and USTCON and missing proofs. Expanders. Error reduction using expanders.

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November 7 2008
Error reduction using expanders. Explicit constructions of expanders and USTCON in L.

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November 12 2008
Explicit constructions of expanders and USTCON in L. Derandomization using pseudorandom generators.

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November 14 2008
Derandomization and the Nisan-Wigderson pseudorandom generator.

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November 19 2008
The Nisan-Wigderson pseudorandom generator. Error correcting codes.

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November 21 2008
Error correcting codes. Local decoding and hardness amplification.

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November 26 2008
Local decoding, list decoding and hardness amplification.

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November 28 2008
Interactive proofs. IP=PSPACE.

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December 3 2008
Probabilistically Checkable Proofs. NP is in PCP(nO(1),O(1)).

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December 5 2008
Linearity Testing. PCP: Overview and degree reduction.

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December 10 2008
PCP: Gap amplification.

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December 12 2008
PCP: Alphabet reduction. Conclude course and talk about exam.

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