# All Questions

**3**

votes

**1**answer

193 views

+50

### Lie algebra of invariant polynomials or invariant smooth functions

Is there a symplectic structure on $M_{2n}(\mathbb{R})$, not necessarily with constant coefficients, such that the space of smooth invariant functions, those smooth functions $f:M_{2n}(\mathbb{...

**32**

votes

**0**answers

843 views

+50

### History: What was the Lemma? (Grothendieck Harvard Lectures; Mumford)

In an article about the life of Grothendieck, available here:
http://www.ams.org/notices/200409/fea-grothendieck-part1.pdf
Allyn Jackson writes about how Mumford was profoundly impressed:
Mumford ...

**3**

votes

**1**answer

210 views

+50

### Intuition behind the definition of the Siegel-Eichler transformation

Recently I am reading Wall's paper "On the Orthogonal Groups of Unimodular Quadratic Forms II". In this paper, I encountered with the map $E^1_\omega$, which now I am interested in.
Let $X$ be an ...

**4**

votes

**1**answer

162 views

+150

### Seeking very regular $\mathbb Q$-acyclic complexes

This question was raised from a project with Nati Linial and Yuval Peled
We are seeking a $3$-dimensional simplicial complex $K$ on $12$ vertices with the following properties
a) $K$ has a complete $...

**4**

votes

**0**answers

109 views

+50

### Hierarchical (Recursive) Random Walk Model

Consider the following hierarchical (recursive) random walk model, which is also known as the hierarchical hidden Markov model in computer science.
For the first level $\ell=1$, let $\{X_t^{(\ell)}...