# Special Topics Course: Complexity Theory (2023)

This is a discussion based course where students are expected to learn by themselves and advance the course through discussions during the lecture hours.

The lectures hours are:

- Mon 10.00 to 11.30
- Tue 11.30 to 01.00

The venue is 7/105.

## Meetings

### 24-04-2023

BK: Conclusion and future directions.

### 18-04-2023

DC (DD): Descriptive complexity conclusion.

### 17-04-2023

CC (GV): Data structure lower bounds from communication complexity.

### 11-04-2023

AC (BK): Brent’s formula depth reduction.

### 10-04-2023

AC (BK): VF-completeness of Narayana’s cows polynomials.

### 03-04-2023

AC (RN): VP0 and VNP0. Connections to integer computation.

### 27-03-2023

AC (GS): Shamir’s O(log(n)) computation of factorial using arithmetic operations with integer divide.

### 21-03-2023

DC (DD): FO queries, “reduction” from connected-ness to reachability using FO.

### 20-03-2023

AC (RN): Computing numbers, complexity upper and lower bounds. Factorial.

### 14-03-2023

CC (GV): Asymmetric communication complexity. k-subsets vs all subsets disjointedness.

### 13-03-2023

BK: Ryser’s formula for permanent.

### 28-02-2023

AC (GS): Baur-Strassen Theorem.

### 27-02-2023

AC (GS): Division elimination, computing partial derivatives.

### 21-02-2023

DC (SN): Interpretation, free variables, validity of formulas under interpretations.

### 20-02-2023

CC (GV): Lower bound methods for deterministic cc: Fooling sets.

### 13-02-2023

SC (BK): NC and AC classes. Addition in AC⁰. Regular languages in NC¹.

### 31-01-2023

AC (RN): Homogenization lemma, division elimination using truncated series.

### 30-01-2023

DC (DD): Vocabulary for strings. FO formulas for addition.

### 24-01-2023

CC (GV): Balancing protocol trees to log(number of leaves)-depth. Protocol from matrix decomposition that is not a protocol.

### 23-01-2023

SC (BK): Non-uniform models, Boolean circuits, Does SAT have small circuits? Karp-Lipton theorem.

### 17-01-2023

CC (GV): Definition of deterministic communication complexity, protocol trees, matrix decompositions, combinatorial rectangles, and f-monochromatic rectangles. Lower bound for equality using combinatorial rectangles.

### 16-01-2023

AC (RN): Definitions of determinant, permanent, circuits, formulas, ABPs and IMM. Poly-size circuits and ABPs (via IMM) for elementary symmetric polynomials (recurrence).

DC (DD): Vocabulary, structures, first-order formulas. Example: Vocabulary for directed graphs with designated source and sink. FO formula for undirected graphs and no loops.

### 12-01-2023

We discussed interactive proofs and saw one for the “Graph Non-Isomorphism” problem. We decided on the topics split for future discussions. Also, a 6-hour per-week work schedule is set for each student.

### 09-01-2023

We discussed the implications of SAT is in P. A poly-time algorithm for SAT would imply poly-time algorithms for, given any fixed number of alternating quantifiers, checking whether a given quantified Boolean formula with that many alternating quantifiers is true or false. Notice that this problem is much more general than SAT. The class of problems poly-time, many-one reducible to any of these generalizations of SAT is called PH.

### 02-01-2023

I presented an overview of various specialized topics in computational complexity theory.