Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

8
votes
0answers
199 views

Commuting matrix variety $[A,B]=0$ - can one geometrically explain divisibility of $F_ q$ point count by high powers of $q$?

$\DeclareMathOperator\Comm{Comm}\DeclareMathOperator\Id{Id}$Consider the variety $\Comm$ of commuting matrices $[A,B]=0$ over some field $K$. It is much studied, and interesting for various reasons. ...
2
votes
0answers
100 views

On an exercise in The Probabilistic Method : random dilate of a set in a finite field

This is related to Problem $4.6$ in ``The Probabilistic Method'' by Alon and Spencer, where one essentially has to prove the following: Let $p$ be a prime, and $A$ be any subset of $\mathbb{F}_p$. ...
1
vote
1answer
164 views

Is there an analogue of the Balazard-Saias-Yor criterion for the Riemann Hypothesis for finite fields?

The Balazard-Saias-Yor criterion for the Riemann Hypothesis states that the latter is equivalent to the statement that $$\int_{\Re(s)=1/2} \frac{\log|\zeta(s)|}{|s^2|}|ds|=0$$ where $\zeta$ denotes ...
-2
votes
0answers
94 views

On the sum $\sum_{x=0}^{(p-1)/2}(\frac{x^{4n}+cx^{2n}+d}p) $ with $p$ an odd prime

Let $p$ be an odd prime, and let $n$ be a positive integer. For $c,d\in\mathbb Z$ we define $$F_p^{(n)}(c,d):=\sum_{x=0}^{(p-1)/2}\left(\frac{x^{4n}+cx^{2n}+d}p\right),$$ where $(\frac{\cdot}p)$ is ...
0
votes
0answers
79 views

A series of conjectures on $\sum_{x=0}^{(p-1)/2}(\frac{x^5+cx^3+dx}p)$ (II)

As in Question 319254, for an odd prime $p$ and integers $c,d$ we let $$S_p(c,d):=\sum_{x=0}^{(p-1)/2}\left(\frac{x^5+cx^3+dx}p\right).$$ If $p\equiv1\pmod4$, then we obviously have \begin{align}&\...
0
votes
0answers
85 views

Is there a notion of linear $\mathbb F_q[x]$ program?

A feasibility linear integer program is essentially deciding if a convex polytope represented by a set of inequalities has an integer point and a minimization linear integer program is to find the ...
-1
votes
1answer
246 views

Write the algebra closure of $F_p$ as union of finite fields [closed]

This question follows Field theory by Steven Roman, Chapter 9, Exercise 20. Denote the algebraic closure of the finite field $F_q$ by $\Gamma(q)$, and let $a_n$ be any strictly increasing infinite ...
0
votes
2answers
198 views

Permutations of squares and finite fields

Let $S_n$ be the symmetric group of all permutations of $\{1,\ldots,n\}$, and let $$S(n)=\bigg\{\sum_{k=1}^nk^2\pi(k)^2:\ \pi\in S_n\}.$$ Motivated by Question 316142 of mine, here I ask the following ...
6
votes
1answer
203 views

Covering the finite plane with lines

This is, essentially, a geometrically rendered version of the question I asked a week ago, with the emphases slightly shifted; it seems more natural and appealing (to me, at least) in this form. Let ...
2
votes
0answers
140 views

On the set $\{\sum_{k=1}^n \lambda_ka_k:\ a_1,\ldots,a_k\ \text{are distinct elements of}\ A\}$

For a field $F$ let $p(F)=p$ if the characteristic of $F$ is a prime $p$, and $p(F)=+\infty$ if $F$ is of characteristic zero. In 2007 I considered the linear extension of the Erdos-Heilbronn ...
4
votes
2answers
286 views

Non-torsion part of the abelianisation of congruence subgroups

I've posted this question on math.stackexchange, but haven't gotten any responses so I'm trying here instead. Let $A = F_q[T]$ be the ring of polynomials in one variable with coefficients in a finite ...
0
votes
0answers
35 views

Computing with a vector subspace equipped with a prescribed basis over finite fields

Let $U$ be a subspace of the finite dimensional vector space $V$ over a field $\mathbb{k}$. Let $B_V$ and $B_U$ be fixed bases for $V$ and $U$ respectively. Let $u \in U$ and let's give ourselves $[u]...
4
votes
1answer
269 views

Submersion implies many rational points in image?

Let $A \colon V \to W$ be a surjective linear map (defined over $\mathbb{Z}$), inducing a projection $\alpha \colon \mathbb{P}(V) \to \mathbb{P}(W)$. Let $X \subseteq \mathbb{P}(V)$ and $Y \...
2
votes
0answers
124 views

The growth of class number in $\mathbb{Z}_p$-extensions of function fields

Let $X$ be a curve (proper, smooth, ...) over a finite field $\mathbb F_q$ where $q$. Suppose also that $\mathbb F_q$ contains the $p$-th roots of unity, in this case we have the following (unique) ...
2
votes
0answers
85 views

Polynomials passing through points with tangential conditions

In corollary here http://math.mit.edu/~lguth/Exposition/erdossurvey.pdf on polynomial methods it is said "(Parameter counting) If $S\subset\mathbb F^n$ is a finite set, then there is a non-zero ...
5
votes
0answers
94 views

$\mathbb{F}_q$-rational elements in unipotent classes of a finite group of Lie-type

I've tried posting this question on MSE, but didn't manage to get an answer there, so I'm trying again here. Sorry in advance if this question is trivial or trivially false. I haven't managed to find ...
2
votes
1answer
222 views

The minimum rank of a matrix over GF(2) when part of non-zero off-diagonal elements are set to be zero

Given an $n\times n$ matrix $A$, whose elements are over $GF\left(2\right)$ and all diagonal elements are $1$. There are $m\ (m\leq n^2-n)$ non-zero off-diagonal elements in $A$. If we are allowed to ...
6
votes
1answer
236 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 ...
1
vote
1answer
189 views

Factorisation of polynomials over finite field

Is there a method to factorise a polynomial, for $k \leq m$ and $a_i \in \mathbb{F}_p$, $$ 1 + t^k(1 + a_1 t + a_2 t + \ldots + a_m t^m)^k $$ as a product $$ (1 + t^k)^{x_1} \cdots (1 + t^l)^{x_l} \...
12
votes
2answers
337 views

Roots of lacunary polynomials over a finite field

If $P$ is a polynomial over the field $\mathbb F_q$ of degree at most $q-2$ with $k$ nonzero coefficients, then $P$ has at most $(1-1/k)(q-1)$ distinct nonzero roots. Does this fact have any standard ...
6
votes
1answer
141 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, {...
1
vote
1answer
101 views

Lifting Lang-Steinberg to DVR's in Characteristic 0

Let $A$ be a compact DVR in characteristic $0$, uniformizer $\pi$ and residue field $k$. Let $A\subset B$ be a complete DVR with the same uniformizer $\pi$ and algebraicly closed residue field $F$. ...
2
votes
0answers
163 views

Intersection of two varieties in $\mathbf{F}_q^n$

Suppose we identify $\mathbf{F}_q^n$ with $\mathbf{F}_{q^n}$. Let $X_n$ be the irreducible hypersurface defined by $Nx=1$ where $N$ is the norm map. There is an analogous hypersurface $X_{n-1}$ in $\...
6
votes
1answer
249 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} $...
0
votes
0answers
186 views

Are the integers a vector space or algebra over “some” field or over “some” ring?

Every vector $v$ in a finite-dimensional vector space space $V$ of dimension $n$ over a field $F$ has a unique representation in terms of a basis ${\frak B} \subseteq V$, where a basis for $V$ is a ...
4
votes
0answers
72 views

Monoid cohomology of $\mathbb{N}$ for a linear algebraic group

Let $k$ be a finite field and $k_E:=k((X))$ denote the field of Laurent series over $k$. We define a Frobenius endomorphism on $k_E$ via $f(X)\mapsto f(X^p)$. We choose a lift $\varphi:k_E^{sep}\...
5
votes
2answers
239 views

Surjectivity of norm map on subspaces of finite fields

It is basic that the norm map $N:\mathbf{F}_{q^n}^* \to \mathbf{F}_q^*$ is surjective for finite fields. In fact $N(x) = x^{(q^n-1)/(q-1)}$. How well does this simple fact extend to subspaces? A ...
1
vote
0answers
76 views

Decomposition of a Matrix by Sparse Matrices

Let $\mathbb{F}$ is a field. Consider an $n \times n$ matrix $\bf A$ over $\mathbb{F}$. $\bf A$ is called sparse matrix over $\mathbb{F}$ iff the number of non-zero entities of $\bf A$ be at most ...
1
vote
1answer
61 views

Notions of convergence over extensions of finite fields

Let $\displaystyle Q_p[x] = \left\{\frac{p(x)}{q(x)} \mid \, p(x),q(x) \in \mathbb{F}_p[x], \, q(x) \neq 0 \right\}$ denote the field of fractions extending $\mathbb{F}_p[x]$. If we consider the ...
3
votes
1answer
142 views

Solving system of multivariable algebraic equations over $\mathbb Q$ by reducing over $\mathbb F_p$

I try to solve the finite system of multivariable algebraic equations with coefficients from $\mathbb Q$. It would be sufficient for me to prove that there is only finite number of solutions over $\...
1
vote
1answer
129 views

Pair of vectors multiplied by a random matrix and its inverse transpose are distributed randomly up to their dot product

Given arbitrary nonzero vectors $\vec{x}_1, \vec{y}_1, \vec{x}_2, \vec{y}_2 \in \mathbb{Z}^{n}_p$ ($p$ prime) with $\langle x_1, y_1 \rangle = \langle x_2, y_2 \rangle$, I am trying to show that: $(...
1
vote
0answers
66 views

Reference request: Number of elliptic and hyperbolic quadratic forms of a given rank over a finite field

My question is over the finite field $\mathbf{F}_q$ of $q$ elements. It is well known that a symmetric matrix of odd rank corresponds to a parabolic quadratic form but even rank symmetric matrices ...
2
votes
1answer
161 views

Alternate descriptions of finite fields

The finite field of order $p^n$ is isomorphic to $(\mathbb Z/p \mathbb Z)[X]/(P)$, where $P$ is an irreducible polynomial in $(\mathbb Z/p \mathbb Z)[X]$ of degree $n$. This describes every finite ...
2
votes
0answers
31 views

Lacunary fully reducible polynomial over a finite field

The following problem is motivated by this MO question on rich directions determined by a set of a finite plane. Problem Does there exist a constant $C$ such that for all odd primes $p$ there is a ...
4
votes
1answer
165 views

Balancing points with lines

$\newcommand{\F}{\mathbb F}$ Suppose that $p$ is a prime, and $k<p/2$ a positive integer. Consider a system of $k$ distinct directions in the affine plane $\F_p^2$, and the system of $k$ pencils ...
1
vote
0answers
121 views

On primitive roots of the form $5^k+10^m$ with $k$ and $m$ nonnegative integers

Let $p$ be any prime. It is well known that the set $$G_p=\{0<g<p:\ g\ \text{is a primitive root modulo}\ p\}$$ has cardinality $\varphi(p-1)$, where $\varphi$ is Euler's totient function. It is ...
6
votes
1answer
207 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 ...
4
votes
0answers
170 views

When spreading out a scheme, does the choice of max ideal matter?

I'm looking at Serre's paper How to use Finite Fields for Problems Concerning Infinite Fields. Specifically I'm trying to use the techniques in the proof of Theorem 1.2 to write out the details of the ...
7
votes
1answer
392 views

Linear permutations commuting with $x\rightarrow x^{-1}$

Let $F = \operatorname{GF}(2^n)$ be a finite field. Define a permutation $\phi:F \rightarrow F$ by the formula $$ \phi(x) = x^{-1}, \ x\neq 0; \ \phi(0) =0. $$ We say that a permutations $\psi$ of $F$ ...
8
votes
1answer
368 views

How many rich directions does a set in $\mathbb F_p^2$ determine?

$\newcommand{\F}{\mathbb F}$ A subset $P$ of the affine plane $\F_p^2$ is said to determine a direction if there is a line in this direction containing at least two points of $P$. A set of size $|P|&...
1
vote
1answer
139 views

Is the Adjoint Action self dual over finite fields?

Given a finite group $G$, and representation $\rho: G \to H(\mathbb{F}_q)$ where $H$ is some classical algebraic group ($Gl$, $Sl$, $O$, $SO$, $SP$, $GSP$, $U$, etc), is the induced Adjoint ...
2
votes
0answers
78 views

Trace of Symmetric matrices in fixed rank

I am solving some problem related to symmetric matrices over a finite field $\mathbb{F}_q$ and I am stuck at the following problem: For every $a\in\mathbb{F}_q $, let $S_a(t,m)$ be the set of all $m\...
4
votes
0answers
243 views

How many conjugacy classes of elementary abelian subgroups of rank $2$ does $GL_{n}(Z / pZ)$ have?

Let $p$ be a prime number and $G=GL_n ( \mathbb{Z} / p \mathbb{Z} )$. Consider the set $U$ of upper-triangular matrices of $G$ having entries of $1$ on the diagonal. The cardinality of $U$ is $p^{\...
15
votes
0answers
250 views

Do we expect abelian varieties (and “Artin motives”) to generate the Grothendieck ring of varieties over a finite field?

The Tate conjecture implies that the category of motives over a finite field is generated (as tensor category) by the motives of abelian varieties and Artin motives. See [1] for details. Let $K(\...
1
vote
1answer
47 views

An Extension of an $\operatorname{MDS}$ Code over $\operatorname{GF}(2^q)$

Let $q$ be a power of $2$. Assume that elements of the finite field $\operatorname{GF}(q)$ are denoted by $\beta_i$ for $0\leq i \leq q-1$. We divide elements of $\operatorname{GF}(q)$ in two parts ...
0
votes
4answers
382 views

Show that sets are equal

Let $X=\{x_1,x_2,...,x_n\}$ and $Y=\{y_1,y_2,...,y_n\}$ be sets over a finite field $F$ with $p=char(F)>2$. Assume $$x_1^k+x_2^k+...+x_n^k=y_1^k+y_2^k+...+y_n^k,\ 1\leq k\leq n$$ I wanna ...
1
vote
0answers
106 views

Roots of polynomials over Z/p^kZ

Over a finite field, such as Z/pZ, the number of roots of a polynomial is no larger than the degree. I'm interested in how does this generalize to Z/p^kZ. I'm sure that this has been looked at, but I ...
6
votes
1answer
233 views

Herbrand-Ribet and Mazur-Wiles for function fields

Is there a version of Herbrand-Ribet or Mazur-Wiles (relating divisibility of class groups to special values of L-functions) for functions fields (over finite fields)? Probably the proofs would have ...
1
vote
1answer
82 views

Generalization of a field norm to the linear group

I've been struggling with this question for some days now. Let $K$ be a field extension of $k$, and $x$ an invertible linear transformation of the $K$-vector space $V$. If we consider $V$ as a $k$-...
7
votes
1answer
190 views

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 $\...