Questions tagged [finite-fields]

A finite field is a field with a finite number of elements. For each prime power $q^k$, there is a unique (up to isomorphism) finite field with $q^k$ elements. Up to isomorphism, these are the only finite fields.

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The Lang isogeny

Let $G$ be a connected commutative algebraic group over $\mathbb{F}_q$. If $\text{Fr}_q : G \to G$ denotes the $q$-Frobenius morphism, we define the Lang isogeny $L_q$ to be the endomorphism of $G$ ...
Justin Campbell's user avatar
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Supersingular curves over $\mathbb{F}_q$ and the splitting of $p$

I'm looking at chapter 4 of Waterhouse's "Abelian varieties over finite fields"; and Theorems 4.1 and 4.2 seem to use the following fact: Suppose that $E/\mathbb{F}_q$ is an elliptic curve ...
Rdrr's user avatar
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Source for embedding multiplicative group of an algebraic closure of a finite field?

It's easy to embed the (cyclic) multiplicative group of a finite field into the multiplicative group of $\mathbb{C}$ (or other algebraically closed field of characteristic 0): assign to a generator of ...
Jim Humphreys's user avatar
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1 answer
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Supersingularity and Roots of Unity of Zeta Functions

Let $C$ be smooth projective curve defined over a finite field $\mathbb{F}_q$. Let $$Z(C,u)=\exp(\sum_{n \ge 1} N_r(C) u^r/r) \in \mathbb{Z}[[u]]$$ be its zeta function, where $N_r$ is the number of $\...
Ofir Gorodetsky's user avatar
7 votes
2 answers
302 views

When is Chevalley Warning's bound best possible?

Chevalley Warning's theorem (a form of) states that any homogeneous form over a finite field of degree $d$ in more than $d$ variables has a nontrivial zero in the field. However, for diagonal forms, ...
LASV's user avatar
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When are arithmetic and geometric monodromy equal?

Let $f: Y\to X$ be a finite separable morphism of curves over the finite field $\mathbb{F}_q$. Is there a simple condition under which the arithmetic and geometric monodromy of the covering are equal (...
Mehdi Tibouchi's user avatar
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584 views

On a matrix problem in the field $\mathbb F_2$

Given $M$ a symmetric matrix in $\mathbb F_2^{n\times n}$ having $\mathsf{det}_\mathbb R(M)\neq0$ (non-singular in reals) and satisfying $PMP'=(M+J+I)$ or $P(M+J+I)P'=M$ where $P$ is a permutation ...
Turbo's user avatar
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What are some open problems regarding elliptic curves in finite fields?

I accept that my question seems so vague and broad, and I already looked into some similar questions in MO. But I would like to learn specifically about some open problems and conjectures regarding ...
terett's user avatar
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Fast Vandermonde matrix multiplication over finite field

Let $V_{i,j}=x_i^j$ where $x_i\in\mathbb F_q$ for $1\le i\le n,1\le j\le n$ be a Vandermonde matrix over finite field $\mathbb F_q$. I wish to know the currently known fastest algorithms for ...
tckwok's user avatar
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When is $f(x^d)$ irreducible?

Let $f(x)$ be an irreducible polynomial of degree $n$ over a finite field $\mathbb F_p$. What can we say about $f(x^d)$? When is it irreducible ?
ssp's user avatar
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Representations of $\operatorname{Sp}(2g,\mathbb{Z}_3)$

Let $V$ be a $2g$-dimensional vector space over $\mathbb{Z}_3 := \mathbb{Z}/3\mathbb{Z}$. First, $\operatorname{Sp}(2g,\mathbb{Z}_3)$ acts on $\Lambda^2(V)$, and this decomposition is reducible, as ...
Quentin Faes's user avatar
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2 answers
417 views

How to count the number of tensors over a finite field of tensor rank $r$?

For simplicity, work over $\mathbb F_2$ and only consider order-$3$ equilateral tensors. For $r\in\mathbb Z_{>0}$, how many tensors $\mathfrak{T}\in\mathsf{Ten}_{n}^{\otimes 3}(\mathbb F_2)$ are ...
Yihan Zhang's user avatar
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request sources about self-dual cyclic codes

X. Kai and S. Zhu in the paper "On cyclic self-dual codes", AAECC, vol. 19, pp. 509-525, 2008, at page 510 in line 6 said that, It is well Known that there are no cyclic self-dual codes over $F_q$ ...
Zahra Taheri's user avatar
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1 answer
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Smoothness of the moduli space of Drinfeld modules

I'm studying the proof of Thm 1.5.1. in Laumon's "Cohomology of Drinfeld Modular Varieties". Notation: $\mathfrak{m}$ is a square zero ideal of $\mathcal{O}$ and $k=\mathcal{O}/\mathfrak{m}$. Laumon ...
bad mathematician's user avatar
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Gelfand-Tsetlin bases for Lie groups over finite fields

There is a method of constructing representations of classical Lie algebras via Gelfand-Tsetlin bases. It has also been applied to Symmetric groups by Vershik and Okounkov. Does anybody know of any ...
Roman Fedorov's user avatar
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2 answers
462 views

A quadratic form

Let $q$ be a power of 2. Let $P$ be the set of polynomials in $F_q [x]$ of degree d or less. Let $\mathbb{Z}$ be the ring of integers. For any $f \in P$, let $\psi(f)$ be the number of distinct ...
user3208's user avatar
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Given $v,w$ primes of $k$, is there $K/k$ so $K_v\cap\Bbb Q^\text{cycl}=K_w\cap\Bbb Q^\text{cycl}=K\cap\Bbb Q^\text{cycl}$?

For any field $k$, let $\mu(k)$ denote the roots of unity in $k$. Now let $k$ be a number field and let $v, w$ be non-archimedean primes of $k$ with distinct residual characteristics. Does there ...
Joel Dodge's user avatar
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Upper bound for an exponential sum involving characters of a finite field

Let $q = p^n $ be a prime power, $\alpha\in\mathbb{F}_{q} $ a primitive element of the finite field $\mathbb{F}_q$ and denote by $\chi $ a non-trivial additive character of $\mathbb{F}_{q} $. Set $\...
nahila's user avatar
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Calculus over finite fields

$P(x,y,z)$ is a polynomial function on an algebraic surface $S$ in $F_{q}^{3}$. Suppose that the derivative of $P$ along any tangent vector of $S$ is zero. Can we say that $P$ is constant on $S$? ...
Ben's user avatar
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Easy bound on number of points on a variety over a finite field

Let $V$ be a closed algebraic set in $\mathbb{A}^n$ defined over a finite field $K$, with irreducible components $Z_1,\dotsc,Z_m$. Let $D = \sum_i \deg Z_i$ and $d = \max_i \dim Z_i$. Then $$|V(K)|\...
H A Helfgott's user avatar
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Polynomial representation of modular arithmetic in finite fields

Let $n \in \mathbb{N}$ be a predefined integer. Consider the following bijection (between the ring of integers modulo $2^n$ and finite field with $2^n$ elements: $$ \phi: \mathbb{Z}_{2^n} \to \mathbb{...
Konstantce's user avatar
7 votes
0 answers
124 views

Removing rows to reduce the rank

What is the smallest number of rows one can delete from a matrix to reduce its rank (by $1$)? Is there any standard name / notation for this characteristic? Has it been studied? I am in fact ...
Seva's user avatar
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259 views

Cyclic shift acting on finite Grassmannian

The (twisted) cyclic shift $(v_1,v_2,\ldots,v_n) \mapsto (v_2,v_3,\ldots,v_n,(-1)^{k-1}v_1)$ acting on the Grassmannian $\mathrm{Gr}(\mathbb{C};k,n)$ of $k$-planes in $\mathbb{C}^n$ is an important ...
Sam Hopkins's user avatar
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200 views

Groupoid cardinality of DM stack and point counting on coarse moduli spaces

Let $X$ be a finite type DM stack over a finite field $k$ with a coarse moduli space $X_c$. (We only assume $X_c$ is an algebraic space and $X$ might have infinite inertia stack.) Under which ...
Maxim P.'s user avatar
7 votes
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128 views

Sum of densities of support of $A$ and $A^{-1}$ for $A=1+\dots\in \mathbb F_2[[x]]$

Let $A=1+\dots\in\mathbb F[[x]]$ be a (multiplicatively) invertible series over the field $\mathbb F_2$ of two elements. Writing $A=\sum_{n\geq 0}\alpha_n x^n$ and $\frac{1}{A}=\sum_{n\geq 0} \...
Roland Bacher's user avatar
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How can I solve a cubic equation in a finite field with characteristic 2?

I need to solve the usual cubic equation $x^3 + ax^2 + bx + c = 0$ over a finite field $GF(2^n)$. This is to avoid doing a brute-force Chien search in a BCH decoder. I read in a paper about an easy ...
Dimitri's user avatar
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3 answers
907 views

Hypersurface missing just one point

Let $\mathbb F_q$ be a finite field and $n$ an integer. What is the minimal degree $d = d(q,n)$ of a polynomial $f \in \mathbb F_q[X_1,\dots,X_n]$ such that the set $Z(f)$ of zeros of $f$ in the ...
Joël's user avatar
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6 votes
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751 views

Exponential sums over finite fields with even characteristic

I am looking for an elementary evaluation (if one exists) of the exponential sum $$ G_r(a,b) = \sum_{x \in \mathbb{F}_{2^r}} \psi(ax^2 + bx), $$ where $a,b \in \mathbb{F}_{2^r}^*$ are both units, $\...
David's user avatar
  • 197
6 votes
2 answers
653 views

existence of an elliptic curves with given number of points over finite field

Is there a theorem which guarentees the existance of an elliptic curve with given number of points over $\mathbf{F}_p$ for a given $p$. Thanks
Himanshu Shukla's user avatar
6 votes
1 answer
497 views

Finite field "contour" sum

Let $\Bbb{F}_q$ be a finite field. Choose a non-square $\delta \in \Bbb{F}_q^*$ and form the quadratic extension $\Bbb{F}_q\big( \sqrt{\delta} \, \big)$. For an element $z \in \Bbb{F}_q\big( \sqrt{\...
Jeanne Scott's user avatar
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6 votes
2 answers
467 views

How do the number of plane curves over a finite field of a fixed genus increase with the degree?

Let $k$ be a finite field. We define $N(d,g)$ to be the number of plane curves $f(x,y)$ defined over $k$ of degree $d$ with (geometric) genus $g$. If $D(d) := (d-1)(d-2)/2$ (the maximum possible ...
Victor Miller's user avatar
6 votes
2 answers
3k views

Quotient of $Z[x_1,...,x_n]$ by a maximal ideal is a finite field [duplicate]

I am seeing the proof of the Ax-Groethendieck theorem from commutative algebra and I have a problem. How can I prove that if $x_1,...,x_n$ are complex numbers and $I$ is a maximal ideal of $\mathbb{Z}[...
Hugo Rafael Oliveira Ribeiro's user avatar
6 votes
1 answer
332 views

2-Torsion in Jacobians of Curves Over Finite Fields

Let $C$ be a (smooth, projective) curve over a finite field $\mathbb{F}_q$, and let $J_C(\mathbb{F}_q)$ denote its Jacobian. Suppose the genus $g$ of $C$ is at least $1$. Question 1: Are there curves ...
Ofir Gorodetsky's user avatar
6 votes
1 answer
300 views

Which criteria for "uniformly splitting" polynomials?

Let $P(x)$ be an irreducible monic polynomial of degree $\ge4$ with integer coefficients. We all know that over a finite field $\mathbb F_p$, $P$ will often split, and I am interested in polynomials ...
Wolfgang's user avatar
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6 votes
1 answer
11k views

Number of n-th roots of unity over finite fields [closed]

How many $n$-th roots of unity does a finite field $\mathbb{GF}\left(p^k\right)$ have? ($p$ is prime). And then kind of related to that, is there a finite field with exactly $n_1,\ldots,n_N$ $n_1$-th,....
Anadim's user avatar
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6 votes
2 answers
398 views

Good and bad reduction for twists of algebraic curves

Suppose we have two curves $C/\mathbb{Q}$ and $C'/\mathbb{Q}$ which are twists of each other i.e. they are isomorphic over a field extension $K/\mathbb{Q}$. Suppose that $C$ has good reduction at a ...
did's user avatar
  • 595
6 votes
1 answer
172 views

Smallest set of nonzero vectors in $\mathbb F_2^n$ which intersects every 2-dimensional subspace

What is the smallest set of nonzero vectors in $\mathbb F_2^n$ which intersects every 2-dimensional subspace? For example, for n = 3, the set {001, 010, 011} does the job, and is minimal. For n = 4, {...
JacobS's user avatar
  • 61
6 votes
1 answer
591 views

Upperbounding a sum of Legendre-Symbols

Let $p$ be a prime with $p\equiv 3 \mod 4$, for any $\mathcal{I} \subset \lbrace 0,...,p-1 \rbrace $ and any $\mathcal{J} \subset \lbrace 0,...,p-1 \rbrace $ with $\vert\mathcal{I}\vert \leq \sqrt{p} $...
nahila's user avatar
  • 93
6 votes
3 answers
418 views

On the rank of a matrix $S$ with coefficients in $\mathbb F_{2^m}$

Let $\mathbb F$ be a finite field with characteristic 2 and let $S \in M(2k, 2k, \mathbb F)$ be the matrix defined as follows $$ S=\left[\begin{array}{ccccccc} 0 & \...
Sfarla's user avatar
  • 307
6 votes
2 answers
861 views

Does there exist a polar decomposition of matrices over finite fields?

There exists a polar decomposition for matrices over the reals. What I would like to know is if an analog has been shown for groups of matrices over finite fields. If not, it would be great to get ...
gnat79's user avatar
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6 votes
1 answer
364 views

Least prime in Artin's primitive root conjecture

Let $a$ be an integer which is neither a square nor $-1$. Artin's conjecture states that there are infinitely many primes $p$ for which $a$ is a primitive root modulo $p$. My question is whether there ...
Dr. Pi's user avatar
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6 votes
1 answer
367 views

Polynomiality of functions over residue rings

Suppose $\mathbb{Z}/m \mathbb{Z}$ is a residue ring for some $m \in \mathbb{N}$. If $m=p$ is a prime number then every function $f:\mathbb{Z}/p \mathbb{Z} \rightarrow \mathbb{Z}/p \mathbb{Z}$ is a ...
user35603's user avatar
  • 411
6 votes
2 answers
308 views

Polynomials over $\mathbb F_2$ without zeros in $\mathbb F_2$ having an inverse series with support of large density.

Does there exist a sequence $A_n=A_n(x)\in\mathbb F_2[x]$ over the field $\mathbb F_2$ of two elements (represented by $0$ and $1$) such that $A_n(0)=A_n(1)=1$ and the inverse series $1/A_n=\sum_{j=0}...
Roland Bacher's user avatar
6 votes
1 answer
304 views

Number of points on a linear algebraic group over a finite field

Let $G$ be a linear algebraic group defined over a finite field $\mathbb{F}_q$ as a variety of dimension $d$. What would be a good, simple lower bound for $G(F_q)$? One can get something fairly nice ...
H A Helfgott's user avatar
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6 votes
1 answer
429 views

Étale fundamental group of multiplicative group over an algebraically/separably closed field

This is a repost of my question here. Do we know the structure of the étale fundamental group $\pi^\text{et}_1(\mathbb{G}_{m,K^\text{sep}})$ of the multiplicative group, for a given field $K$? For ...
Pippo's user avatar
  • 291
6 votes
1 answer
492 views

Do you know which is the minimal local ring that is not isomorphic to its opposite?

The most popular examples are non-local rings and minimal has 16 elements. I am interested in knowing examples of local rings not isomorphic to their opposite.
José María Grau Ribas's user avatar
6 votes
1 answer
242 views

Enumerating subspaces of $\mathbb{F}_q^n$ in terms of words and inversions

When $q$ is a prime power, then on the one hand the $q$-binomial coefficient $\binom{n}{k}_q$ equals the number of $k$-dimensional subspaces of $\mathbb{F}_q^n$, and on the other hand it is the ...
Martin Brandenburg's user avatar
6 votes
1 answer
368 views

Enumeration of field generators of a finite field over $\mathbb{F}_{q}$, which are $m^{th}$ powers in the same field

Consider the finite field extension $\mathbb{F}_{{q}^{d}}$ over $\mathbb{F}_{q}$, where $q=p^a$ for some prime $p$. We assume $d\geq 2$. Let, $$ S=\{ \alpha \in \mathbb{F}_{q^d}\hspace{0.1 cm} | \...
Riju's user avatar
  • 430
6 votes
1 answer
274 views

If number of points on a manifold is $q^n ( [n+1]_q )$ does it imply a geometric relation to $A^n (P^n)$?

Consider an algebraic manifold whose number of points is $q^n ([n+1]_q)$. Is there a geometric relation to $A^n (P^n)$? In particular, is there an equivalence in the Grothendieck ring of varieties ...
Alexander Chervov's user avatar
6 votes
1 answer
444 views

Vector with many non-zero coordinates

Given finite field $\mathbb{F}_q$, positive integers $n$ and $k<n$. Given $k$-dimensional subspace $X$ of $\mathbb{F}_q^n$, for which $m=m(q,k,n)$ may we find for sure a vector in $X$ with at least ...
Fedor Petrov's user avatar

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