Log rank conjecture is one of the most famous open problems in the area of communication compleixty.

Lets consider the two party cdommunication complexity. Alice and Bob have $n$ bit strings $a,b$ , respectively, and they wish to compute arbitrary boolean function $f(a,b)$.

Communication matrix of $f$ is a $2^{n}\times 2^{n}$ matrix whose indices of row (column) corresponds to the inputs of Alice (Bob) and each entry $M_f (a,b)$ correspond to function value $f(a,b)$.

Log rank conjecture asserts that $CC(f) = (\log rank (M_{f}))^{O(1)}$

On the other hand, rank is a crucial role in the linea algebra and similar concepts of rank are considered.

QUESTION:I am looking for similar conjectures in the area of communication compleixty and related compleixty theoretic areas, similar-seeming conjectures without the communication complexity machinery, similar-seeming conjectures in linear algebra.Is there an appropriate reference ?

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    $\begingroup$ I don't understand what you are asking. You have stated the log rank conjecture. Are you looking for consequences, for similar conjectures in related areas, similar-seeming conjectures without the communication complexity machinery, or something else? $\endgroup$ Commented May 23, 2013 at 9:25
  • $\begingroup$ Matrix rigidity asks about the least amount of perturbation required to substantially lower the rank of a matrix. Maybe that'd interest you. $\endgroup$ Commented May 23, 2013 at 19:48

1 Answer 1


The log-rank conjecture is equivalent to the following conjecture.

For any graph $G$ with adjacency matrix $A$ and complement graph $\bar{G}$, the chromatic number of $\bar{G}$ is at most $(\log \mathsf{rank}(A))^{O(1)}$.

This is from Lovasz and Saks's original paper, which has more connections.

Nisan and Wigderson observed that to prove the log-rank conjecture it suffices to show that any $M \in \{0, 1\}^{N \times N}$ has a monochromatic rectangle of size at least $N 2^{-(\log \mathsf{rank} M)^{O(1)}}$.

More intuitively, the hardness in trying to disprove the conjecture comes from the fact that it's difficult to construct a non-trivial example of a binary matrix that has low rank over the reals. The trivial examples are matrices that can be decomposed into a small number of combinatorial rectangles, but we know that such a decomposition implies small communication complexity. So the conjecture asks, are all low rank binary matrices decomposable into a small number of rectangles.


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