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Questions tagged [randomness]

Randomness is a key component of probabilistic algorithms, many combinatorial aarguments, the analysis of hashing functions, and in cryptography, among other applications.

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0 votes
1 answer
134 views

Parity of the sum of pseudorandom bits over a non-sparse set of inputs

Suppose I have a pseudorandom function (in the theoretical sense) $X\colon\{0,1\}^{n+m}\rightarrow\{0,1\}$ (where $m$ is polynomial in $n$) and a non-empty set $S\subseteq\{0,1\}^m$ ($S$ is not sparse,...
2 votes
1 answer
280 views

What kind of string is produced by successive application of argmax M

Fix a version of Solomonoff's universal distribution $\mathbf M$ and consider the following procedure for generating an infinite binary sequence $\omega$. Start with some $\omega_0$. Each subsequent ...
11 votes
1 answer
367 views

Theorem 2.4(i) in Valiant-Vazirani paper "NP is as easy as detecting unique solutions"

I have a question about the paper "NP is as easy as detecting unique solutions" by Valiant and Vazirani, specifically the proof of the Theorem 2.4(i). The proof starts by saying Clearly, $...
3 votes
2 answers
222 views

Do pseudo-random number generator test batteries have any theoretical grounding?

There are a lot of PRNG test batteries, like DieHarder. They do check that some statistical tests expected for random sequence are indeed present. But is there any theoretical motivation, why this ...
7 votes
1 answer
576 views

Connectivity of a random regular graph of degree $d$

An Erdős–Rényi graph over $n$ vertices and average degree $d$ is not connected w.h.p. iff $d < \log n$. I was wondering for what the degree $d$ would a random regular graph of degree $d$ be ...
0 votes
0 answers
33 views

What’s the difference between P-computable distributions and P-samplable distributions?

$\newcommand{\calC}{\mathcal{C}} \newcommand{\calD}{\mathcal{D}} \newcommand{\calE}{\mathcal{E}}$ I have two questions and the first one is presented in the title. The second one is about the ...
4 votes
1 answer
156 views

Are there any problems in $\mathsf{BPP}$ that are known to be $\mathsf{RP}$-hard or $\mathsf{coRP}$-hard?

It's suspected that probabilistic complexity classes such as $\mathsf{RP}$ or $\mathsf{BPP}$ don't have complete problems. Of course, their promise counterparts have complete problems, but I am not ...
3 votes
0 answers
132 views

Inverse of leftover hash lemma

Leftover hash lemma: Let $X$ be a random variable over $X \in {\mathcal {X}}$ and let $m>0$. Let $h: {\mathcal S} \times {\mathcal X} \rightarrow \{0,1\}^m$ be a 2-universal hash function. If $m \...
0 votes
0 answers
72 views

Are there any examples of problems in ZPP not yet in P? [duplicate]

Is there a problem of which we can prove that it is in ZPP but we don’t yet know whether it’s in P or not?
2 votes
1 answer
388 views

Chernoff bound for weighted sums of Bernoulli random variables

I tried to prove the following Chernoff-type bound when doing research, and found that it is of indepent interest. Let $X_1, \dots, X_n$ be independent random varibles such that each $X_i$ is a ...
13 votes
3 answers
2k views

Expected number of random comparisons needed to sort a list

Consider the task of sorting a list x of size n by repeatedly querying an oracle. The oracle draws, without replacement, a random pair of indices (i, j), with i != j, and returns (i, j) if x[i] < x[...
44 votes
7 answers
6k views

Truly random number generator: Turing computable?

I am seeking a definitive answer to whether or not generation of "truly random" numbers is Turing computable. I don't know how to phrase this precisely. This StackExchange question on "efficient ...
1 vote
0 answers
250 views

Converse form of Chernoff bound

Suppose $X_1,\ldots,X_n$ are i.i.d. random variables, all with mean $p$, and we have the statement that $\Pr\left[\sum_i X_i\geq 0.8n\right]\geq 0.9$, can we use this to conclude anything about $p$ (...
5 votes
1 answer
298 views

Hardness assumption: an NP-complete problem whose ratio of hard instances do not tend to zero?

I am wondering about the following property $\text{(P)}$ of an $NP$-complete language $L$ $\begin{align}\exists M\text{ a polytime machine}\lim_{n\to\infty}P(\text{M solves a random instance of size $...
0 votes
1 answer
135 views

Derandomizing arbitrary width *read-many* and *ordered* branching programs?

Modifying following TedP We know that derandomizing width $5\leq k\in O(1)$ read many branching programs is equivalent to $BPNC^1=NC^1$ and derandomizing width $k\in\Omega(n)$ read once ordered ...
7 votes
2 answers
128 views

Shoup-style hashing without one-wayness

Let $H$ be an almost universal hash family of functions from $D^2$ to $D$. For any functions $f,g \in H$ define the function $\langle f,g \rangle : D^4 \to D$ by $\langle f,g \rangle(a,b,c,d) \...
0 votes
0 answers
122 views

Creating a random tree (BST) on $n$ elements using a random sequence of zeroes and ones

We have a sorted list of $n$ numbers and we shall create a BST for these numbers. We create a random sequence of zeroes and ones of length $n$. We shall make use of this random binary sequence to form ...
1 vote
0 answers
115 views

Random variates generation in discrete-event simulation models

In discrete-event simulation, most university textbooks (e.g., Law & Kelton, Banks etc.) state that for generating variates for each random variable (e.g., interarrival time, service time etc.) in ...
2 votes
2 answers
189 views

Finding a random regular graph with degree d

I'm trying to find undirected random graphs $G(V,E)$ with $|V|$ = $d^2$ for $d \in \mathbb{N}$ such that $\forall v \in V: deg(v) = d$. For $d \in 2\mathbb{N} +1$ this trivially is impossible as no ...
0 votes
2 answers
1k views

Password checking algorithm

Usually to check password validity we used to create over given password it hash value and compare it with stored one. So password protection relies on strength of hashing function. Could it be used ...
11 votes
0 answers
286 views

Provable BPP Hierarchy

No Time Hierarchy theorem is known for $\mathsf{BPTIME}$, however, consider the following simple modification of the definition: A language is in $\mathsf{ProvableBPTIME}[f(n)]$ if there is a ...
3 votes
1 answer
226 views

Converting a Bernoulli to a Gaussian

It is not hard to see that, given one sample from a univariate unit-variance Gaussian $X\sim \mathcal{N}(\mu,1)$ with unknown $\mu$ s.t. $0<|\mu|\leq 1$, one can simulate one draw from a "...
4 votes
1 answer
201 views

Generating $k$ random bits from a pdf with entropy $H(p) = k$

All the sources online say that, intuitively, a distribution with entropy $k$ has $k$ bits of pure randomness in it. So can we formalize this as follows? Suppose I can only sample from my distribution,...
0 votes
1 answer
230 views

Upper bound on Independence Number of Random Regular Graph with degree $\Theta(\sqrt{|V|} \log^2 |V|)$

Let $G=(V,E)$ be a random $\Delta$-regular graph with $\Delta \in \Theta(\sqrt{|V|} \log^2 |V|)$. I'm analysing an algorithm having asymptotic running time crucially depending on the Independence ...
1 vote
1 answer
315 views

How come Wikipedia says that Random Turing Machines can provide uncomputable output?

Wikipedia article mentioned : Hypercomputation The third paragraph starts off with: Technically, the output of a random Turing machine is uncomputable; however, most hypercomputing literature focuses ...
37 votes
1 answer
1k views

Efficiently computable function as a counter-example to Sarnak's Mobius conjecture

Recently, Gil Kalai and Dick Lipton both wrote nice articles on an interesting conjecture proposed by Peter Sarnak, an expert in number theory and the Riemann Hypothesis. Conjecture. Let $\mu(k)$ ...
13 votes
2 answers
381 views

Is there an assumption that implies $P=ZPP$ which is not known to imply $P=BPP$?

There are assumptions that are known to imply that $P = BPP$. For example, if there exists a function in $E = DTIME(2^{O(n)})$ that has circuit complexity $2^{\Omega(n)}$, then $P = BPP$ [1]. Clearly, ...
9 votes
1 answer
326 views

The power of randomized logspace with two-way access to the random tape

Let $\mathsf{ZPL}$/$\mathsf{RL}$/$\mathsf{BPL}$ denote the classes of the languages which are accepted (with zero/one-side/two-side error) by a logspace Turing machine with one-way access to the ...
0 votes
0 answers
76 views

Randomized Reduction for Maximization Problem

I have two maximization problems $P_1$ and $P_2$ where the decision version $L_1 = \{(x, t) : \operatorname{Val}_1(x)\ge t\}$ of $P_1$ is $\mathsf{NP}$-complete. Let $f:P_1\to P_2$ be a randomized ...
-1 votes
1 answer
246 views

Does two-sided error have more capability than one-sided error?

From $P=RP$ extrapolation we might think $EXP=REXP$. What evidence do we have $BPP\subseteq REXP$? What consequence $REXP\subseteq BPP$ gives other than what $EXP\subseteq BPP$ gives?
4 votes
0 answers
146 views

BPP fragment of a PSPACE complete problem

Consider a PSPACE-complete problem (e.g., TQBF). Is there a sub-problem in BPP, that is not known to be in P? Is there a general technique of finding such sub-problems? Are any of them "natural" (i.e....
13 votes
2 answers
3k views

Sum of Independent Exponential Random Variables

Can we prove a sharp concentration result on the sum of independent exponential random variables, i.e. Let $X_1, \ldots X_r$ be independent random variables such that $Pr(X_i < x) = 1 - e^{-x/\...
0 votes
0 answers
87 views

Expected value of a random experiment in a graph

I need to find the expected value of R in the random experiment below. $$ R = \frac{1}{K} \sum_{C \in \mathcal{H} } \ [\frac{1}{2} |V(C)| * (|V(C)| - 1) - |C|] $$ $\mathcal{H}$ is a partition on ...
2 votes
1 answer
125 views

Lower bound on the worst-case unbiased coin flips to sample a distribution?

Say that we have a distribution $\mathcal{D}$ such that all probabitilities associated with it are $p$-bit fixed precision numbers, so: $$ \Pr_{X\sim \mathcal{D}}[X = k] =\sum_{i = 1}^p \frac{k_i}{2^i}...
12 votes
1 answer
522 views

Deterministic error reduction, state-of-the-art?

Assume one has a randomized (BPP) algorithm $A$ using $r$ bits of randomness. Natural ways to amplify its probability of success to $1-\delta$, for any chosen $\delta>0$, are Independent runs + ...
2 votes
1 answer
511 views

How to use a 𝑝-coin so a TM can decide an undecidable language in polynomial time? [closed]

In "Computational complexity- A modern approach" book (page 117) for the lemma 7.12 (following) the author mentioned that if the ρ is efficiently computable ρ-coin cannot give probabilistic algorithm ...
2 votes
1 answer
98 views

Robustness to non-uniform randomness vs. one-sidedness

Consider any problem where, fixing two (disjoint) subsets $\mathcal{Y},\mathcal{N}\subseteq \{0,1\}^n$ of the input space, the goal is to obtain a randomized algorithm $D$ which, given a uniformly ...
3 votes
1 answer
264 views

Optimal bounds for $k$-wise non-uniform random bits

Let $k\geq 2$ be a constant (in my case, $k=4$), and $n,t \geq 0$ be integers such that $2^t \leq n$. What is the smallest sample space (or, equivalent, how many true independent random bits are ...
6 votes
1 answer
373 views

Error reduction with expanders and derandomization

In "standard" error reduction with an expander, if a randomize algorithm uses $n^d$ random bits, we need $n^d+O(n)$ random bits to achieve $2^{-O(n)}$ error probability. Now, if the algorithm has a ...
8 votes
8 answers
4k views

Best way to determine if a list of bytes are random?

Is there some algorithm out there that can return some value indicating a level of randomness? I believe it's called Data Entropy. I recently read this article: http://faculty.rhodes.edu/wetzel/...
4 votes
1 answer
190 views

Strong seeded randomness extractors with low entropy loss

I would like to implement a strong seeded randomness extractor for flat sources as a part of my project. Most of the literature on seeded extractors is concentrated on minimizing seed length. ...
5 votes
1 answer
259 views

Newman's lemma for distributional communication complexity

This may be obvious — sorry if it is. Newman's lemma (Newman91] shows that any public-coin communication protocol to compute a Boolean function $f\colon \{0,1\}^n\times\{0,1\}^n\to\{0,1\}$ can be ...
0 votes
1 answer
61 views

What forms of randomness are 'allowed' in FPRASs?

I cannot seem to find a source describing randomized approximation schemes ((F)PRAS) that tells me exactly what sort of randomness a program is allowed to use. A priori it seems to me that being able ...
22 votes
1 answer
497 views

Random functions of low degree as a real polynomial

Is there a (reasonable) way to sample a uniformly random boolean function $f:\{0,1\}^n \to \{0,1\}$ whose degree as a real polynomial is at most $d$? EDIT: Nisan and Szegedy have shown that a ...
2 votes
2 answers
204 views

Multiple independent random number streams

Having multiple streams of pseudo-random numbers known to be independent and with a uniform distribution I want to do Monte Carlo simulations in parallel. In other words, one thread will have a full-...
5 votes
1 answer
170 views

Sets of solutions which it is hard to uniformly sample from, but easy to integrate functions over? (Or compute expectations over?)

I'm curious if there is a problem (e.g. something like perfect matchings on a given graph, number of solutions to a boolean equation, etc. for precise frameowork see JVV86) such that: 1) It is hard ...
5 votes
1 answer
472 views

Distributions which are intractable to sample from?

I'm looking for an interesting family of probability distributions $P$ that is intractable to efficiently sample from. I'm not sure what the right notion of intractable is, though I know the notion ...
4 votes
0 answers
162 views

research problem for undergraduate majoring in Computer Science and Mathematics

I am wondering if somebody can suggest a small research problem for undergraduate majoring in Computer Science and Mathematics. Would love to work with random matrices or wavelets.
1 vote
0 answers
142 views

Proof of Sipser-Lautmann Theorem

I have written the following answer as an attempt to prove a variation of Sispser-Lautmann theorem, but it was rejected without any comments. I would appreciate if anyone can find the flaws in this ...
2 votes
1 answer
210 views

Motivation for randomness extractors

I'm a maths masters student exploring how results in the geometry of finite fields, such as the finite field Kakeya conjecture, applies to randomness extractors. I'm not a computer scientist, and must ...