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Questions in which polynomials (single or several variables) play a key role. It is typically important that this tag is combined with other tags; polynomials appear in very different contexts. Please, use at least one of the top-level tags, such as nt.number-theory, co.combinatorics, ac.commutative-algebra, in addition to it. Also, note the more specific tags for some special types of polynomials, e.g., orthogonal-polynomials, symmetric-polynomials.

1 vote
0 answers
261 views

One-sided version of the "best approximation polynomial" : Upper polynomial approximations

Let $X$ be a finite subset of $\mathbb R$ and let $f : X \to {\mathbb R}$. Suppose we want to approximate $f$ by a polynomial $g$ of fixed degree $d\geq 1$ with the additional condition $g\geq f$. Let …
Ewan Delanoy's user avatar
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3 votes
3 answers
595 views

Every positive polynomial with rational coefficients is above a completely Q-factorized nonn...

This question was originally asked in stackoverflow (https://math.stackexchange.com/questions/103941/every-positive-polynomial-is-above-a-completely-q-factorized-positive-polynomial) but as it has rem …
Ewan Delanoy's user avatar
  • 3,595
17 votes
4 answers
988 views

Finite interpolation by a nondecreasing polynomial

It is well known that there are polynomials that "interpolate" in that $f(x_i)=y_i$ for all $i$, and the Lagrange interpolating polynomial even warrants a solution of degree $ < n$. …
Ewan Delanoy's user avatar
  • 3,595
4 votes
2 answers
874 views

Is it true that all the "irrational power" functions are almost polynomial ?

Hello all, the $\Delta$ operator on functions $\mathcal{N} \to \mathbb{R}$ (where $\mathcal N$ denotes $\lbrace 1,2, \ldots , \rbrace$ )defined by $\Delta(f)(n)=f(n+1)-f(n)$ is well-known and it is …
Ewan Delanoy's user avatar
  • 3,595
8 votes
0 answers
492 views

"Consecutive" irreducible polynomials

If $P\in {\mathbb Z}[X]$ is a polynomial of degree $2$, then it is easy to see that for any integer $m$, at least one of the polynomials $P-(m+1),P-(m+2),P-(m+3),P-(m+4)$ is irreducible in ${\mathbb Z} …
Ewan Delanoy's user avatar
  • 3,595
3 votes
3 answers
292 views

Expressing field inclusions by polynomial equalities on coefficients

Let $A$ be the set of all quadruples $(a_0,a_1,a_2,a_3) \in {\mathbb Q}^4$ such that the polynomial $P=X^4+a_3X^3+a_2X^2+a_1X+a_0$ is irreducible and if $z$ is any root of $P$, then ${\mathbb Q}(z)$ c …
Ewan Delanoy's user avatar
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2 votes
2 answers
1k views

algebraic numbers of degree 3 and 6, whose sum has degree 12

This question is related to Degree of sum of algebraic numbers. Forgive me if this is a dumb question, but are there two algebraic numbers $a$ and $b$ of degree $3$ and $6$ respectively, such that the …
Ewan Delanoy's user avatar
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5 votes
0 answers
190 views

"Unknot" algebraic set defined by two mutually dependent set of variables

Let $n$ be an integer $\geq 4$, and let $V \subseteq {\mathbb C}^{2n-1}$ be the set of all $(a_1,a_2, \ldots ,a_n,b_1,b_2, \ldots ,b_{n-1}) \in {\mathbb C}^{2n-1}$ such that the derivative of the pol …
Ewan Delanoy's user avatar
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12 votes
3 answers
2k views

Growth of the "cube of square root" function

Hello all, this question is a variant (and probably a more difficult one) of a (promptly answered ) question that I asked here, at Is it true that all the "irrational power" functions are almost polyn …
Ewan Delanoy's user avatar
  • 3,595
6 votes
2 answers
604 views

What is the set of possible values of the degree of the sum of two algebraic numbers with fi...

This question is related to Degree of sum of algebraic numbers and algebraic numbers of degree 3 and 6, whose sum has degree 12. In this last question I asked a very special case of the following p …
Ewan Delanoy's user avatar
  • 3,595
8 votes
1 answer
599 views

Integer polynomial (of degree >1) all of whose values are square-free

Is there an integer polynomial $ A \in {\mathbb Z} [ X ]$ of degree $d\geq 2$ such that for any integer $n\in {\mathbb Z}$ , $ A(n) $ is a square-free integer?
Ewan Delanoy's user avatar
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1 vote
2 answers
339 views

Infinite collection of elements of a number field with very similar annihilating polynomials

In other words, we are asking for infinitely many elements in $B$, whose minimal polynomials are ``as similar as possible". …
Ewan Delanoy's user avatar
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15 votes
2 answers
566 views

Which polynomials arise as formulas for a conjugate

For any integer $r \geq 2$, et $V_r$ be the set of polynomials $Q \in {\mathbb Q}[X]$ of degree $r-1$ such that there is an algebraic number $\alpha$ of degree $r$ , such that $Q(\alpha)$ is a conjugate … It is not hard to see that $V_2$ consists exactly of $X$ and all the polynomials $a_0-X$, for $a_0\in {\mathbb Q}$. Have the $V_r(r \geq 3)$ been studied? Is anything known about $V_3$ ? …
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