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Questions tagged [fourier-analysis]

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13
votes
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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 $f: \{0,1\}^n \to \{0,1\}$, ...
10
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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
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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 $...
7
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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
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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
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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
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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
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0answers
110 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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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 \...
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50 views

relations between the degrees of a boolean function and its absolute function

Given a boolean function $f:\{0,1\}^n\rightarrow\mathbb{R}$ of degree $d$, is there any upper bound in terms of $d$ on the degree of the function $|f|$, where $|f|(x)=|f(x)|$. Here the degree of $f$ ...
1
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0answers
77 views

Agnostic query learning of decision trees

Gopalan, Kalai, Klivans gave an algorithm https://dl.acm.org/citation.cfm?id=1374376.1374451 for agnostically learning decision trees $h:\{0,1\}^n\to\{0,1\}$ under the uniform distribution given ...
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0answers
66 views

Relative Two-Function Hypercontractive Inequality $\langle T_{\rho\sigma} f,g \rangle \le \langle T_{\sigma} f,g \rangle^q$

The hypercontractive theorem (or Bonami Beckner inequality) says (Ryan O'Donnell): This of course also directly gives the 'intermediate' inequality $\|T_{\rho\sigma}f\|_q \le \|T_\sigma f\|_{1+(q-1)\...
1
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0answers
75 views

Fourier expansion of boolean functions and affine subspaces

Let $f:\mathbb{F}^n_2\rightarrow \{0,1\}$ be a function constant on an affine subspace $V$ of co-dimension $t$. Assume that that $V$ is a linear subspace, by replacing $f(x)$ with $f(x+v)$ for some $v ...
1
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0answers
31 views

Are there uses for a Fourier transform of length $n^m$ with elements of maximum size $n$?

In essence, I'm trying to get a better feel for when there is a use for FFT with small coefficients, compared to the length, assuming that we get a better runtime. I've been toying with an idea for a ...
1
vote
0answers
90 views

Period of a Multivariable Function using Quantum Computing

consider a function $$f(x_1,x_2...x_n)$$ I am told it is possible to compute the period of the function as a vector $$<l_1,l_2...l_n>$$ where each l denotes the period of the function for ...
0
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0answers
39 views

Hidden subgroup problems in a tower of subgroups

Let $H$ be a hidden subgroup of $G_1$ that is indistinguishable from subgroup $H^{\prime}$ by quantum Fourier sampling. Now take a larger group $G_2$ such that it contains $G_1$. Now if I do quantum ...
0
votes
0answers
124 views

Determining if a function is constant or not using period finding

Consider an arbitrary boolean function $$f: {\lbrace 0,1 \rbrace}^n \rightarrow \lbrace 0,1 \rbrace$$ which we write as: $$f(x_1, x_2 ... x_n) $$ where each $x_i$ is a boolean variable We note ...
0
votes
0answers
126 views

Computing the period of a function using a quantum computer

Consider a blackbox function $$f(x): Z \rightarrow \lbrace 0,1 \rbrace $$ Which inputs an integer and outputs 0 or 1 with bit complexity n. If the period P of this function satisfies $$P \in O(2^{...