# Questions tagged [integral-quadratic-forms]

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**3**

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### Similar reduced integral matrices

Let $d\geq 1$ be an integer. I'm not assuming anything here about $d$ (it is not necessarily squarefree, for example)
For all $a,b,c\in\mathbb{Z}$ such that $ac-b^2=d,$ set $[a,b,c]_d=\begin{pmatrix}...

**12**

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**2**answers

1k views

### On Siegel mass formula

I have asked this question exactly here. The question is as follows:
I am interested deeply in the following problem:
Let $f$ be a (fixed) positive definite quadratic form; and let $n$ be an ...

**3**

votes

**1**answer

88 views

### Normalizing trains without sign walking in compartments

Consider the quadratic form $5x^2+6y^2$. This has Conway Sloan $2$-adic symbol $[1^{-1}2^{-1}]_0$. After a sign walk from $1$ to $2$ the symbol becomes $[1^{+1}2^{+1}]_4$. However, there doesn't exist ...

**0**

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**0**answers

89 views

### p-adic numerical analysis question for a quadratic form

Let $A$ be a symmetric matrix with even diagonal and elements in $\mathbb{Z}_p$ and nonzero discriminant. (Yes, $p$ can be two) and $a$ an nonzero integer. Suppose there exists a solution to $x^{\top}...

**5**

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**1**answer

221 views

### Are stably equivalent quadratic forms over Z equivalent?

Let $Q_1, Q_2, R$ be quadratic froms over $\mathbb{Z}$ such that $Q_1 \oplus R \cong Q_2 \oplus R$ as quadratic forms. Is it necessary that $Q_1 \cong Q_2$?
I know that by Witt's theorem it is true ...

**2**

votes

**1**answer

223 views

### Indefinite Ternary Forms with Square Discriminant

Is there any general theory to find the numbers represented by ternary forms of the type
$q(x,y,z)=ax^2+bx^2-abz^2,$
when $a,b$ are prime?
By doing an internet search, the closest I found was the ...

**3**

votes

**2**answers

301 views

### Paper of Denis Simon on quadratic equations in dimensions 4, 5?

In several places I have come across references to a 2005-6 preprint of Denis Simon entitled
Quadratic equations in dimensions 4, 5, and more
This paper gives fast algorithms to find isotropic ...

**0**

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**1**answer

84 views

### Lower bounds on the rank of a unimodular lattice, given the binlinear pairing of a subset of basis vectors

I have some questions on lower bounds on the rank of unimodular lattices given the bilinear pairing of a subset of its basis is known.
Let $\Lambda$ be an odd, unimodular matrix of signature $(1,T)$. ...

**3**

votes

**3**answers

202 views

### A question on an involution of $E_8$ lattice

There exits an involution $\iota$ of the $E_8$ lattice such that $(E_8)^{\pm} \cong D_4$, where $(E_8)^{\pm}$ denotes the $\pm$ eigen-lattice of the involution $\iota$. Could someone kindly give me an ...

**1**

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**0**answers

155 views

### Orthogonal transformations with trivial spinor norm as product of reflections $r_w$ with $(w,w)=-2$

I'm trying to prove that, for a standard unimodular even lattice $\Lambda$ (by standard I mean that it is direct sum of copies of the hyperbolic plane $U$ and $E_8$) every element of $O^+(\Lambda)$, i....