User Sergey Dovgal

29 answers

251 votes

87k views

314 bookmarks

Mathematical games interesting to both you and a 5+-year-old child

Sep 18, 2017 at 21:29

65 answers

138 votes

32k views

152 bookmarks

Important formulas in combinatorics

co.combinatorics big-list

Aug 17, 2015 at 8:59

1 answer

55 votes

5k views

42 bookmarks

IMO 2017/6 via arithmetic geometry

ag.algebraic-geometry arithmetic-geometry

Jul 25, 2017 at 20:14

2 answers

45 votes

4k views

24 bookmarks

The two ways Feynman diagrams appear in mathematics

ct.category-theory mp.mathematical-physics monoidal-categories string-diagrams

Dec 3, 2017 at 9:23

16 answers

43 votes

7k views

28 bookmarks

What does the generating function $x/(1 - e^{-x})$ count?

co.combinatorics lie-algebras hopf-algebras bernoulli-numbers

Dec 18, 2009 at 1:44

3 answers

18 votes

1k views

8 bookmarks

What is the probability that two random permutations have the same order?

co.combinatorics asymptotics symmetric-groups random-permutations

Feb 5, 2016 at 12:15

1 answer

15 votes

980 views

2 bookmarks

Existence of double eigenvalue

linear-algebra matrices eigenvalues

Jan 1, 2018 at 16:18

1 answer

14 votes

643 views

6 bookmarks

For a stable matrix $B$ and anti-symmetric $T$, such that $B(I+T)$ is symmetric, show that $\mbox{tr}(TB)\leq0$

linear-algebra matrices mp.mathematical-physics stochastic-processes stochastic-differential-equations

Dec 5, 2017 at 22:07

2 answers

12 votes

1k views

9 bookmarks

Eigenvalue perturbation theory via Feynman diagrams

linear-algebra matrices eigenvalues perturbation-theory

Oct 17, 2017 at 13:19

2 answers

11 votes

1k views

4 bookmarks

Proofs of some combinatorial identities

reference-request co.combinatorics generating-functions combinatorial-identities catalan-numbers

Oct 1, 2017 at 6:01

1 answer

11 votes

483 views

2 bookmarks

Which of these sums appear most often?

nt.number-theory co.combinatorics additive-combinatorics partitions

Jan 3, 2018 at 13:45

1 answer

10 votes

608 views

4 bookmarks

$2 \times 2$ matrix question

linear-algebra matrices

Dec 27, 2017 at 14:34

2 answers

10 votes

774 views

5 bookmarks

Simple question about polynomials

ag.algebraic-geometry co.combinatorics ac.commutative-algebra polynomials

Jan 4, 2018 at 14:30

2 answers

9 votes

730 views

4 bookmarks

Asymptotic difference between a function and its "binomial average"

asymptotics binomial-coefficients real-analysis

Nov 20, 2010 at 21:46

3 answers

8 votes

1k views

3 bookmarks

Optimization problem with determinant as objective

linear-algebra oc.optimization-and-control convex-optimization determinants

Oct 20, 2017 at 5:36

0 answers

6 votes

98 views

4 bookmarks

A conjectured trace inequality for some products of powers of matrices II

linear-algebra

Aug 18, 2017 at 17:19

1 answer

6 votes

261 views

3 bookmarks

Phase transition in matrix

linear-algebra matrices sp.spectral-theory random-matrices

Jan 13, 2020 at 12:45

0 answers

5 votes

186 views

2 bookmarks

a problem about possible generating series

nt.number-theory co.combinatorics

Jul 29, 2017 at 11:08

0 answers

5 votes

176 views

2 bookmarks

How to count Isomorphism Types of arbitrary structures?

co.combinatorics ac.commutative-algebra lo.logic model-theory universal-algebra

Aug 4, 2017 at 22:43

0 answers

4 votes

139 views

1 bookmarks

Using Mellin transform for a certain function

generating-functions integral-transforms catalan-numbers

May 20, 2015 at 15:21

0 answers

3 votes

86 views

1 bookmarks

``de-polarizing" a univariate P-recurrence

co.combinatorics enumerative-combinatorics

Oct 7, 2017 at 20:54

1 answer

1 vote

233 views

2 bookmarks

Nonlinear low-rank approximation - corrected

linear-algebra matrices oc.optimization-and-control convexity norms

Jan 4, 2018 at 22:58

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