Questions tagged [fourier-analysis]

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60
votes
3answers
6k views

Why does Fourier analysis of Boolean functions “work”?

Over the years I have gotten used to seeing many TCS theorems proved using discrete Fourier analysis. The Walsh-Fourier (Hadamard) transform is useful in virtually every subfield of TCS, including ...
42
votes
12answers
4k views

Applications of representation theory of the symmetric group

Inspired by this question and in particular the final paragraph of Or's answer, I have the following question: Do you know of any applications of the representation theory of the symmetric group in ...
29
votes
1answer
2k views

Fourier coefficients Boolean Functions described by Bounded Depth Circuits with AND OR and XOR gates

Let $f$ be a Boolean function and let's think about f as a function from $\{-1,1\}^n$ to $\{ -1,1 \}$. In this language the Fourier expansion of f is simply the expansion of f in terms of square free ...
26
votes
2answers
802 views

What is the complexity of distinguishing a true Fourier spectra from a fake one?

A $PH$ machine is given oracle access to a random Boolean function $f:\{0,1\}^n \to \{ -1,1 \}$ , and two Fourier spectra $g$ and $h$. The Fourier spectra of a function $f$ is defined as $F:\{0,1\}^...
19
votes
2answers
869 views

Linearly independent Fourier coefficients

A basic property of vector spaces is that a vector space $V \subseteq \mathbb{F}_2^n$ of dimension $n-d$ can be characterized by $d$ linearly independent linear constraints - that is, there exist $d$ ...
18
votes
2answers
862 views

Are all the functions whose fourier weight is concentrated on the small sized sets computed by AC0 circuits?

Are all the functions whose fourier weight is concentrated on the small sized sets(or terms with low degree) computed by $\mathsf{AC}^0$ circuits ?
16
votes
2answers
754 views

Robustness of splitting a junta

We say that a Boolean function $f: \{0,1\}^n \to \{0,1\}$ is a $k$-junta if $f$ has at most $k$ influencing variables. Let $f: \{0,1\}^n \to \{0,1\}$ be a $2k$-junta. Denote the variables of $f$ by $...
16
votes
2answers
413 views

An extension of the noise operator

In a problem I am currently working on, an extension of the noise operator arises naturally, and I was curious whether there has been prior work. First let me revise the basic noise operator $T_{\...
14
votes
1answer
523 views

Best query complexity of Goldreich-Levin / Kushilevitz-Mansour learning algorithm

What is the best known query complexity of Goldreich-Levin learning algorithm? Lecture notes from Luca Trevisan's blog, Lemma 3, states it as $O(1/\epsilon^4 n \log n)$. Is this the best known in ...
14
votes
1answer
473 views

Can one prove $\mathsf{PARITY} \notin \mathsf{AC}^0$ using Linial-Mansour-Nisan theorem and the knowledge of fourier spectrum of $\mathsf{PARITY}$?

Result 1: Linial-Mansour-Nisan theorem says that the fourier weight of the functions computed by the $\mathsf{AC}^0$ circuits is concentrated on the subsets of small size with high probability. ...
13
votes
0answers
302 views

Fourier spectrum of the parity of two monotone Boolean functions

This is a question that I've been pondering, on and off, for a while, and unsuccessfully. I'd be very interested in any insight regarding this conjecture. (Or rather, these conjectures.) Recall that, ...
13
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0answers
292 views

Sign patterns for Fourier coefficients of Boolean functions

Given a sequence of real numbers $(a_i)$, the sign-pattern sequence $(s_i)$ is defined by $s_i = +$ if $a_i \geq 0$ and $s_i = -$ otherwise. For a boolean function $f: \{0,1\}^n \to \{0,1\}$, ...
12
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1answer
672 views

The entropy of a convolution over the hypercube

Say we have a function $f:\mathbb{Z}_2^n \to \mathbb{R}$, such that $\sum _{x\in \mathbb{Z}_2^n} f(x)^2 = 1$ (so we can think of $\{ f(x)^2\} _{x\in \mathbb{Z}_2^n}$ as a distribution). It is natural ...
11
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1answer
328 views

Upperbound on the degree of a boolean function in terms of its sensitivity

A very interesting open problem in the study of complexity measures of Boolean function is the so called sensitivity vs block sensitivity conjecture. For background on sensitivity versus block ...
10
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1answer
218 views

Is this “subgroup packing” polytope integral?

Let $\Gamma$ be a finite abelian group, and let $P$ be the polytope in $\mathbb{R}^\Gamma$ defined to be the points $x$ satisfying the following inequalities: $$\begin{array}{cl} \sum_{g\in G} x_g \...
10
votes
0answers
157 views

Variance of bounded functions with rapidly decaying Fourier coefficients

I have the following conjecture about bounded functions on the hypercube. Any help resolving it (proof, counterexample, some ideas) is much appreciated. Conjecture. Let $f : \{ -1, +1 \}^n \to [-1, +...
10
votes
0answers
404 views

Relation beween approximate degree of a function and its Fourier coefficient.

Consider a Boolean function $f:\{0,1\}^n\to\{0,1\}$. The degree of the function $d$ has a clear meaning in term of its Fourier coefficients, there are no weight on coefficient of degree higher than $...
9
votes
1answer
184 views

Has there been any progress in tightening the exponent in the result that polylog independence fools $AC_0$?

Braverman showed that distributions which are $(log \frac{m}{\epsilon})^{O(d^2)}$-wise independent $\epsilon$-fool depth $d$ $AC^0$ circuits of size $m$ by "gluing together" the Smolensky ...
7
votes
1answer
229 views

Is a monotone boolean function monotone as a multilinear polynomial?

Let $f:\{-1,1\}^n \rightarrow \{0,1\}$ be a monotonically increasing boolean function. That is, $f(x) \leq f(y)$, if coordinate-wise $x \leq y$. Now, let $F: [-1,1]^n \rightarrow \mathbb{R}$ be $f$ ...
7
votes
2answers
319 views

Given a subset of the hypercube and a copy translated by s, find s

Problem: Suppose we are given an $n$ element subset $A\subseteq\{0,1\}^d$ of the $d$ dimensional hypercube and a translated copy $B= A+s$ by some secret $s\in\{0,1\}^d$. Find $s$ as fast as possible ...
7
votes
0answers
107 views

Learning function with a few low-order Fourier coefficients, from uniformly random samples

Let $f:\{-1,+1\}^n \to \{-1,+1\}$ be a boolean function where all of the energy of the Fourier transform of $f$ is concentrated in a small number of low-order coefficients, say $k$ coefficients each ...
7
votes
0answers
189 views

An alternative proof of hypercontractivity of the Becker-Bonami operator

The Becker-Bonami operator $T_p$ on a function $f(x) : \{0,1\}^d \to \mathbb{R}$ is defined as follows. Let $\nu(x)$ be a perturbation of $x$ so that every bit remains the same with probability $p$ or ...
7
votes
0answers
135 views

Computing the Fourier-Walsh coefficients of an arithmetic circuit

Given an $f$-fan in arithmetic circuit of depth $d$ over $GF(q)$ (for some prime $q$) and the set of variables $(x_1,\ldots,x_n)$, what is the state of the art upper bound for calculating the Fourier-...
6
votes
1answer
121 views

Average-case analogue of Small-bias Spaces

Recall that an $\epsilon$-biased space is a set $S \subset \{0,1\}^n$ such that for every non-zero linear test $\alpha \in \{0,1\}^n \setminus \{0\}^n$, the expected bias $$| \mathbb{E}_{x \in S} [ (-...
6
votes
2answers
662 views

Is the the spectral norm of a Boolean function bounded by the degree of its Fourier expansion?

Let $f: \{-1,1\}^n \rightarrow \{-1,1\}$ be a Boolean function. The Fourier expansion of $f$ is $$f(T) = \sum_{S \subseteq [n]} \widehat{f}(S)\ \chi_S(T)$$ where $\widehat{f}(S)$ are real numbers ...
6
votes
0answers
123 views

Are there generalizations for Chow's theorem?

The Chow's theorem as it stands holds only for a single linear threshold gate. That these gates are uniquely determined by their first $n+1$ Fourier coefficients. Are there other circuits for which ...
5
votes
1answer
100 views

Majority function stability under deletion and addition of entries

It is well known that the majority function is stable under random flipping of bits. That is, if $v$ is a random binary vector, and then we re-sample each bit of $v$ with probability $\delta$ and get $...
5
votes
0answers
109 views

Is there a simple argument for this Hemi-Icosahedron Boolean function?

This is problem 1(e) from Homework 1 of the course about Analysis of Boolean functions at CMU in 2012 as well as problem 1.1(n) on p.34 of Ryan O'Donnell's Analysis of Boolean Functions. Compute ...
5
votes
0answers
162 views

Fourier Analysis on checking whether there exists a vector in hypercube orthogonal to a set of vectors?

I know virtually noting about Fourier Analysis and I'd like to know whether it's worth to learn this topic for my problem. My problem is: Given vectors $h_1,\cdots,h_k\in\{+1,-1\}^n$ where $k < n$,...
5
votes
0answers
125 views

Truncated convolution algorithm

Suppose I have $n+1$-dimensional vectors $a$ and $b$. For each $i = 0, \dots, n$, I also have integers $0 \leq j_0(i) \leq j_1(i) \leq i$. I want to compute the following variant of a convolution: $$ ...
4
votes
1answer
262 views

$\ell_1$ norm of Fourier coefficients vector for the hypercube

Let $G$ be the normzlied hypercube graph on $2^d$. It is a Cayley graph and it is well known that its eigenvalues are given by $\lambda_r = 1-2\frac{|r|}{d}$ for every $r \in \{0,1\}^d$. Given a ...
4
votes
1answer
91 views

Is being fooled by limited independence preserved by products?

Question. Let $f,g : \{\pm 1\}^n \to \{\pm 1\}$ be $\varepsilon$-fooled by $k$-wise independence -- i.e. for any $k$-wise independent random variable $X$, $\left|\mathbb{E}[f(X)] - \mathbb{E}[f(U)]\...
4
votes
1answer
176 views

Which (almost) balanced Boolean function has smallest “total” influence

The well known Kahn–Kalai–Linial (KKL) Theorem says that for any Boolean function $f\colon \{-1,1\}^n \xrightarrow{} \{-1,1\}$ $$ \max_{i \in [n]} \{\mathbf{Inf}_i[f] \} \geq \mathop{\bf Var}[f] \cdot ...
4
votes
0answers
116 views

Relationship between sparsity and rank of a boolean function

I have the following question when I was going through the proof of the following theorem. Theorem. For XOR function $f \circ XOR$, $rank(M_{f \circ XOR}) = ||\hat f ||_0$ where $M_{f \circ XOR}$ is ...
4
votes
0answers
135 views

About counting the “total size” of non-zero Fourier coefficients of a Boolean function

Given a $f: \{-1,1\}^n \rightarrow \mathbb{R}$, I want to compute this quantity, $\sum_{ \hat{f}(S) \neq 0, S \subseteq 2^{[n]}} \vert S \vert $ i.e the sum of the sizes of the subsets of $[n]$ ...
4
votes
0answers
187 views

How to prove deg(f) = n iff the parity imbalance of f is non-zero?

Not sure if the notation I'm using here is standard or not. I'm going over class notes and I'm stumped over an exercise given: Show that $deg(f) = n \iff PI(f) \neq 0$. Here $f$ is a boolean function ...
3
votes
1answer
153 views

Basic property of boolean functions with restrictions

For $f:\{\pm1\}^n\to\mathbb{R}$, $I\subset\{1,\dots,n\}$ and $x\in\{\pm1\}^{\{1,\dots,n\}\setminus I}$ we define $f_I[x]:\{\pm1\}^I\to\mathbb{R}$ by $f_I[x](y)=f(x,y)$. (We denote by ($x,y$) the ...
3
votes
1answer
135 views

Given a subset of of the hypercube and an affine transform of it, find the affine map

This is a follow up to this resolved question. Suppose we are given a set of bitvectors $A\subseteq\mathbb{F}_2^d$ and an invertible affine transformed copy of it $$B=\{Mx + s\mid x\in A\}$$ for some ...
3
votes
1answer
149 views

Lower bound on the support size of an $\epsilon$-biased distribution

Let $D$ be an $\epsilon$-biased distribution we want to show that $$\text{Supp}(D)\geq \Omega\bigg(\frac{n}{\epsilon^2\log(\frac{1}{\epsilon})}\bigg)$$ I know that there are some proofs for this but I ...
3
votes
1answer
241 views

Nearly Optimal Sparse Walsh-Fourier Tranform

In the recent paper: Nearly Optimal Sparse Fourier Transform[Haitham Hassanieh, Piotr Indyk, Dina Katabi, Eric Price], the authors show an $O(k \log n)$-time algorithm for the problem of computing the ...
3
votes
1answer
168 views

Level $k$ bounds in Analysis of Boolean functions

In Ryan O'Donnell's book Analysis of Boolean functions, following Corollary 9.25 the following appears: If $f\colon \{-1,1\}^n \to \{0,1\}$, and we have $\mathbb{E}[f] = \alpha$, then for any integer ...
3
votes
0answers
154 views

An identity about the Majority function?

Let $f:\{-1,1\}^n \rightarrow \{-1,1\}$ be any boolean function. Let $Maj_n$ represent the majority function. Let $\langle f,g \rangle = E[f(x)g(x)]$ and $\mathcal{I}(f) = E_x[\# i, s.t. f(x)\neq f(x \...
2
votes
1answer
191 views

Fourier decomposition in terms of another basis

Given a Boolean function $f:\{-1,1\}^n\rightarrow \{-1,1\}$, it is well know that the Fourier decomposition of $f$ can be written as $f(x)=\sum_{S\subseteq \{1,\ldots,n\}} \widehat{f}(S) \prod_{i\in S}...
2
votes
0answers
116 views

Sensitivity and Low-Degree Approximation under Non-Uniform Distribution

I am searching for generalizations of analysis of Boolean functions when the input strings are distributed according to a general non-uniform distribution, possibly with arbitrary dependencies between ...
2
votes
0answers
48 views

$p$-biased two-function hypercontractivity

The Hypercontractivity theorem (or Bonami Beckner inequality) is a very useful tool. Unfortunately, it isn't easy to carry over to other spaces than the uniform boolean cube. In Ryan O'Donnel's ...
2
votes
0answers
116 views

What would faster Fourier Transform(FFT?) and/or multiplication algorithms imply?

There are many problems which have implications on P vs. NP and other complexity classes. Supposing that we're interested in Fourier transforms and/or multiplication algorithms, do faster Fourier ...
2
votes
0answers
100 views

On FFT and trigonometric matrix eigenvalues

Let $N=2^n$ for a natural number $n$ and $B$ be the $N\times N$ square matrix of $0$'s and $1$'s $$ B=\begin{pmatrix} 0 & 1 & 0 & \ldots & 0 \\ 1 & 0 & 1 & \ldots ...
2
votes
0answers
150 views

Is the nonnegativeness of a polynomial hard for $\mathsf{NP}_\mathbb{R}$?

It is clear that the following problem is in $\mathsf{NP}_\mathbb{R}$. Input: a list $P$ of triplets $(a,s,t)$ where $s$ and $t$ are nonnegative integers. Output: is there an $x\in \mathbb{R}$ such ...
2
votes
0answers
58 views

Is there a relation between $l_p$-norms of functions with same Fourier spectra but w.r.t different measures on the Hamming cube?

Informally, I want to ask if two functions $f$ and $g$ on the Hamming cube have the same Fourier spectra but w.r.t different measure and basis, then is $||f||_p$ related to $||g||_p$? (Where each $p$-...
2
votes
0answers
102 views

Geometry on a space of polynomial functions

I am considering some geometric concepts in a space of functions.But I am not sure the concept I consider is already defined in some references. Let $P_{1},...,P_{N}:\mathbb{F}_{2}^{n}\rightarrow \...