Unanswered Questions
3,561 questions with no upvoted or accepted answers
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Monotone complexity of s-t connectivity
In the problem CONN, we obtain a directed $n$-vertex graph (encoded as a boolean string of $n^2$ bits, one for each potential edge), and want to decide
whether there is a path between all $n^2$ pairs $...
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46
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Problem unsolvable in $2^{o(n)}$ on inputs with $n$ bits, assuming ETH?
If we assume the Exponential-Time Hypothesis, then there is no $2^{o(n)}$ algorithm for $n$-variable 3-SAT, and many other natural problems, such as 3-COLORING on graphs with $n$ vertices. Notice ...
CommunityBot
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33
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Is BPP= P known for ANY uniform model of computation?
Many believe that BPP $=$ P "should" hold for Turing machines. We even have some "witnesses" for this: otherwise some "strange" things would happen; see e.g. this paper by Implagliazzo and Wigderson.
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32
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Combinatorics of Bellman-Ford or how to make cyclic graphs acyclic?
Roughly speaking, my question is:
How costly is to make a cyclic graph
acyclic while preserving all simple $s$-$t$ paths?
Let $K_n$ be a complete undirected graph on vertices $\{0,1,\ldots,n+1\}$.
(...
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30
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779
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The complexity of checking whether two DAG have the same number of topological sorts
This problem is highly related to the CNF one.
Here is the problem: given two DAG (directed acyclic graphs), if they have the same counting of topological sorts, answer "Yes", otherwise, answer "No".
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29
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Does $EXP\neq ZPP$ imply sub-exponential simulation of BPP or NP?
By simulation I mean in the Impaglazzio-Widgerson [IW98] sense, i.e. sub-exponential deterministic simulation which appears correct i.o to every efficient adversary.
I think this is a proof: if $EXP\...
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28
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523
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Adiabatic quantum computing with level crossings
Question.
In adiabatic evolution, to ensure that the ground state high overlap with the unique ground state of the system (i.e. to achieve arbitrarily small error) using adiabatic theorems, it is ...
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27
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Is Hankelability NP-hard?
I asked this question on SO on April 7 and added a bounty which has now expired but no poly time solution has been found yet.
I am trying to write code to detect if a matrix is a permutation of a ...
CommunityBot
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27
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0
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Counting Isomorphism Types of Graphs
Polya's counting theorem leads to an algorithm for counting (precisely) the number of isomorphism types of graphs with $n$ vertices in $\exp (\sqrt n )$ steps. From Polya theorem you get a formula ...
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26
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696
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Rank mod 6 vs rank over the reals
Let $A$ be a boolean matrix (eg with $0,1$ entries). Assume that $A$ has rank $\le r$ both over $\mathbb{F}_2$ and over $\mathbb{F}_3$. Does this imply that $A$ has low rank over the reals? This seems ...
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23
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Can we do integer addition in linear time?
Why, yes, of course. But I'm actually interested in the cost of computing the sum of multiple integers:
Input: A sequence of nonnegative integers $\langle X_i:i<k\rangle$ written in binary.
Output: ...
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23
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Fine-grained complexity of BPP
If E does not have i.o.-$2^{o(n)}$ circuits, then P=BPP, but this does not tell us about the fine-grained containments between $\mathrm{Time}(n^a)$ and $\mathrm{BPTime}(n^b)$.
Are there reasonable ...
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$\Delta = 57, d=2$ Moore Graph
I am looking into the last open question regarding the existence of Moore Graphs of diameter 2. A problem that has been open in combinatorics for more than 55 years.
You may recall that Hoffman and ...
22
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773
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What is the power of general poly-size permutation branching programs?
Call $\mathsf{PPBP}$ the class of languages decided by poly-size families of permutation branching programs, which are layered branching programs (i.e., the ones defined here) whose transitions ...
21
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Descriptive complexity characterization of TimeSpace classes
Are there descriptive complexity characterizations for TimeSpace complexity classes like $\mathsf{SC^i}= \mathsf{DTimeSpace}(n^{O(1)},O(\lg^i n))$?
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