# Questions tagged [reference-request]

This tag is used if a reference is needed in a paper or textbook on a specific result.

9,219 questions

**25**

votes

**1**answer

434 views

### “Matchmaking website” for project-specific mathematical collaborations [closed]

It seems that even in the age of Internet, most mathematical collaborations are born (and pursued) off-line.
However, I wonder if there exists a "matchmaking website" for mathematical ...

**6**

votes

**1**answer

134 views

### Anisotropic perimeter and regularity of anisotropic minimal surfaces

1. Introduction.
By-now classical results assert that minimal surfaces (in $\mathbb R^n$) are generically "smooth" out of a "small" set.
Question. What are the known regularity results for ...

**8**

votes

**2**answers

629 views

### How to organize collaborations? Managing shared library and LaTeX document

What is an effective way to organize collaborations with several people on the same paper? How do you arrange the $\LaTeX$ document, the shared (digital) papers library, and other aspects?
More in ...

**5**

votes

**2**answers

327 views

### Cases where multiple induction steps are provably required

I am looking for references for theorems of the form:
1) Any proof of theorem $X$ requires $n$ applications of induction axioms
and especially
2) Any proof of theorem $X$ requires $n$ nested ...

**6**

votes

**1**answer

448 views

### Famous but unavailable paper of Jan Boman

The following paper is well known, but hard to find:
J. Boman, $L^p$-estimates for very strongly elliptic systems, Report 29, Department of Mathematics, University of Stockholm, 1982.
In this paper ...

**3**

votes

**0**answers

51 views

### Efficient implementation of the Clifford group for $n$ qubits

I'm looking for an efficient implementation of the Clifford group $\mathcal{C}_n$
of $n$ qubits.
The Clifford group $\mathcal{C}_n$ has stucture $(2_+^{1+2n} \circ C_8).Sp(2,n)$,
where $2_+^{1+2n}$ ...

**-1**

votes

**0**answers

58 views

### Is this expression true? [migrated]

Let $a_1=b_1/h,...,a_n=b_n/h\in\mathbb{R}$ with $h\in\mathbb{R}$ small. It's true that, given a $\alpha\in\mathbb{R}$:
\begin{eqnarray}
(a_1+...+a_n)^\alpha=\sum_{i=1}^n (a_i)^\alpha+\mathcal{O}\left(\...

**2**

votes

**0**answers

59 views

### Algebraic description of the reduced incidence algebra of a poset

In the book "Combinatorial theory" by Martin Aigner (from 1979), the standard algebra of a poset is introduced as the subalgebra of the incidence algebra of a poset consisting of the functions that ...

**11**

votes

**3**answers

506 views

### is this a modular form of some kind?

I suspect that the function
$$F(q) = \sum_{n \geq 0} (2n + 1) \, q^\binom{n+1}{2}$$
may be some kind of modular form. It looks like a weighted theta function, but is not exactly an harmonic theta ...

**22**

votes

**4**answers

720 views

### Is this a known question about the expression of a function on $\Bbb R^2$ as an infinite sum of products?

The question below was posted on Mathematics Stack Exchange. It received no answer, and I do not expect any direct answer to it here. However, the question seems to me a natural one. Thus I wonder ...

**5**

votes

**2**answers

141 views

### Origin of term Ahlfors-David regular

Much of the literature on analysis in metric spaces makes use of an assumption called Ahlfors regularity or Ahlfors-David regularity. Let $q>0$. A metric space $(X,d)$ is Ahlfors(-David) $q$-...

**1**

vote

**0**answers

36 views

### Examples of associative inducers and other inducers

I am curious about how well the following technique can produce algebraic structures and semigroups in particular.
Let $(X,\circ)$ be a semigroup. Let $Y$ be a set and let $L:X\rightarrow P(Y)$ be a ...

**0**

votes

**0**answers

143 views

### Behavior of Ext under base change

Let $x$ be a nonzerodivisor on a local Noetherian ring $(R,m).$ Let $M,N$ be finitely generated $R/xR$-modules.
How to show the existence of the following exact sequence
$\cdots\longrightarrow ...

**4**

votes

**1**answer

67 views

### Sampling uniformly from the vertices of a polytope

I'm looking for a reference on how to sample uniformly (and preferably efficiently, elegantly, etc.) from the vertices of a polytope. I gather that enumerating vertices is hard. I also note the MO ...

**1**

vote

**0**answers

120 views

### On sets of coprime integers in intervals

Briefly,
Question: Is it "good enough" to use least prime factor in choosing a maximal set of coprime integers in an interval?
The post title comes from a 1993 paper of Erdos and Sarkozy. They ...

**4**

votes

**0**answers

113 views

### When does a continuous function's “Fourier series” converge pointwise almost everywhere to the function?

Let $G$ be a compact topological group. By the Peter-Weyl theorem, the complex Hilbert space $L^2(G)$ is the Hilbert space direct sum of the spaces of matrix coefficients of all the irreducible ...

**6**

votes

**0**answers

97 views

### What does it mean for a complex valued function on $G(\mathbb A)$ to be smooth (or smooth of compact support)?

Let $G$ be a linear algebraic group over a number field $k$. Let $\mathbb A$ denote the adeles of $k$, $\mathbb A_f$ the finite adeles, and $k_{\infty} = \prod\limits_{v \mid \infty} k_v$. Here are ...

**0**

votes

**0**answers

40 views

### Existence and uniqueness for semilinear parabolic problem using fixed point approach

Where can I find a proof of existence and uniqueness of solutions for a semilinear parabolic problem
$$u_t -\Delta u +f(t,x,u,\nabla u) =0$$
which is based on a fixed point approach?

**0**

votes

**0**answers

163 views

### Mathematical Problems of General Relativity II

In the introduction of D. Christodoulou's book "Mathematical Problems of General Relativity I", he refers a few times to the second volume. My question is does it exists? Has it been (or will it be) ...

**2**

votes

**0**answers

76 views

### Some questions about cuspidal representations and automorphic representations

My reference is Daniel Bump's book, Automorphic Forms and Representations. $G$ is a connected reductive group over a number field $k$ (in Bump's book he takes $G = \operatorname{GL}_n$). Let $K = K_{...

**3**

votes

**0**answers

80 views

### Gosper's Beta function identities

According to the last paragraph in Mathworld's Beta function article http://mathworld.wolfram.com/BetaFunction.html, Gosper found some multiplication formulas for the Beta function, but it does not ...

**4**

votes

**0**answers

72 views

### Name for facet of a cone containing all but one edge

Let $C \subseteq \mathbb R^n$ be a polyhedral cone, so generated by its edges ($1$-dimensional faces) and $F \subseteq C$ a facet (codimension $1$ face) of it containing every edge except $e$. In ...

**5**

votes

**1**answer

130 views

### An inequality involving $L^1$ and $L^\infty$ norms of a function of a real variable and its derivative

I got to the following inequality by a (hopefully correct) tortuous argument:
If $F:[a,b] \to \mathbb{R}$ is a absolutely continuous monotone function then:
$$ \|F'\|_1^2 \leq 4 \|F\|_1 \, \|F'\|...

**2**

votes

**0**answers

120 views

### Graded Betti numbers $\beta_{n,j}$ for points in $\mathbb{P}^n$

Let $S = \mathbb{C}[z_0, \dots, z_n]$, and let $X$ be a set of points in $\mathbb{P}^n$. I'm looking for references concerning results for the graded Betti numbers $\beta_{n,j}(S/I(X))$, i.e., the ...

**12**

votes

**3**answers

311 views

### (Sharp) inequality for Beta function

I am trying to prove the following inequality concerning the Beta Function:
$$
\alpha x^\alpha B(\alpha, x\alpha) \geq 1 \quad \forall 0 < \alpha \leq 1, \ x > 0,
$$
where as usual $B(a,b) = \...

**5**

votes

**1**answer

126 views

### Reference for showing that $\mathcal{O}(G) \cong U(\mathfrak{g})^{\circ}$ when $G$ is connected and simply connected

Let $G$ be an algebraic group. We can try to reconstruct $G$ from its lie algebra $\mathfrak{g}$, but the best we get in general is a formal group scheme $\operatorname{Spf}(U(\mathfrak{g})^*)$, where ...

**0**

votes

**0**answers

41 views

### Elliptic Dirichlet problems with measure boundary data

Can you point out any references on the Dirichlet problem for divergence-type elliptic operators with a Radon measure as boundary data?

**2**

votes

**1**answer

81 views

### Boundary condition for elliptic problems and domain decomposition

This question is motivated by one that has been previously asked on this website: Elliptic problem on a domain split in two subdomains
Consider an open domain $U$ split in two non-overlapping ...

**2**

votes

**1**answer

108 views

### Difference quotient for functions of bounded variation

Let $u:\mathbb{R}^N \to \mathbb{R}^N$, $u \in BV(\mathbb{R}^N)$, be a function of bounded variation.
We have that the following holds
$$(\ast) \qquad \frac{1}{|B_r(0)|}\int_{B_r(0)} \frac{|u(x+z)-...

**5**

votes

**2**answers

401 views

### Name of a group-like structure

The late Vladimir Arnold, in
Arnold, V., Arithmetics of binary quadratic forms, symmetry of their continued fractions and geometry of their de Sitter world, Bull. Braz. Math. Soc. (N.S.) 34, No. 1, ...

**2**

votes

**0**answers

39 views

### Enumerating lattice points in a product of balls, in limit with dimension

Fix $(L_n)_n$ to be a sequence of lattices, each $L_n\subset \mathbb{R}^n$, where both the effective-inradius and effective-outradius go to 1 (i.e. the Voronoi region of the lattices approach a ball ...

**4**

votes

**2**answers

120 views

### Conjugacy in right-angled Artin groups

I am looking for a reference containing the following result:
Let $a$ and $b$ be two elements of a right-angled Artin group $A$. Assume that $a$ and $b$ have minimal length (with respect to the ...

**3**

votes

**1**answer

182 views

### Elliptic problem on a domain split in two subdomains

Consider the following elliptic problem in a split domain:
$$ (\ast) \quad\begin{cases} -\Delta u=f_1 \quad &\text{ in } U_1\\
-\Delta u =f_2 & \text{ in }
U_2\\
u=g & \text{ on } \...

**3**

votes

**0**answers

76 views

### Jacobian of the action of a matrix on a Grassmannian

I'm looking for a reference concerning a calculation found in Furstenberg's 1963 paper "Non-commuting random products".
Lemma 8.8 of this paper states that if one takes a $d\times d$ invertible real ...

**3**

votes

**1**answer

170 views

### Heuristics for boundary Harnack inequality

What is the heuristic idea of the proof of the boundary Harnack inequality presented in the appendix of Caffarelli's 1998 lectures on the obstacle problem (page 38 here)?

**14**

votes

**2**answers

327 views

### Monoidal functors $\mathcal C \to [\mathcal D,\mathcal V]$ are monoidal functors $\mathcal C \otimes \mathcal D \to \mathcal V$?

It is well known (e.g., Reference for "lax monoidal functors" = "monoids under Day convolution" ) that if $\mathcal C$ is a monoidal $\mathcal V$-enriched category, then a monoid ...

**10**

votes

**1**answer

557 views

### References on dualities on quantum field theory for mathematicians

Dualities on QFT–also called Quantum Field Theory dynamics–is a huge and fundamental research area. However, despite underpinning major mathematical breakthroughs such as the work of Kapustin and ...

**1**

vote

**1**answer

51 views

### encryption with wavelet transform

I need to know about an article, book or other reference that deals with encryption using Fourier transform and the Wavelet. (I plan to use matlab or other recommended software.)

**11**

votes

**1**answer

696 views

### The homology of the orbit space

Suppose we have an acyclic group $G$ and let $X$ be a contractible CW-complex such that $G$ acts freely on $X$ (we do not suppose that the action is proper).
Is there a way to understand the homology ...

**23**

votes

**1**answer

349 views

### Modern survey of unstable homotopy groups?

Toda no doubt made some big strides when computing unstable homotopy groups $\pi_{n+k}(S^n)$ for $k < 20$ which his collaborators later improved upon.
The methods he used are documented in his ...

**1**

vote

**0**answers

48 views

### Filtrations of spectra related to cellular ones and singular homology

I would like to study filtrations of spectra (i.e., objects of the "topological" stable homotopy category $SH$; a filtration of a spectrum $E$ is a sequence of compatible maps $E_{\le i}\to E$) whose ...

**2**

votes

**1**answer

73 views

### Gysin morphism of blow up

Let $X$ be a smooth, projective variety and $i:Y \hookrightarrow X$ a smooth divisor. Let $Z \subset X$ be a proper, closed subvariety disjoint from $Y$. Let $\pi:\widetilde{X} \to X$ be the blow-up ...

**1**

vote

**0**answers

39 views

### Curvature of projection function onto a smooth curve

Suppose we have a smooth curve $C$ lying in $\mathbb{R}^2$, and let us consider the orthogonal projection function $P_C(x)$ onto the curve, described by
$$P_C(x) = argmin_{y \in C} \Vert x - y \Vert$$...

**6**

votes

**1**answer

160 views

### Precise reference for the equivalence of $E_n$ algebras and locally constant factorization algebra?

I've seen the following theorem attributed to Lurie:
Theorem. There is an equivalence of $(\infty,1)$-categories between $E_n$ algebras and locally constant factorization algebra on $\mathbf{R}^n$.
...

**6**

votes

**1**answer

107 views

### Configurations of $n$ points modulo isometries of the ambient space

Let $M$ be a Riemannian manifold and let $n$ a positive integer. Denote by $F_n(M) \subset M^n$ the space of all $n$-tuples of pairwise distinct points from $M$. The isometries of $M$ act co-ordinate ...

**1**

vote

**0**answers

66 views

### Zero-sum games where getting information helps the opponent more

You may know of the paper on the "Memory" game - sometimes the best strategy is turning known cards (here: https://www.math.kth.se/xComb/x1.pdf). Here is a simpler toy example: You and your opponent ...

**3**

votes

**1**answer

114 views

### Divergence of a series related to Schinzel's hypothesis H

The Series
Consider the series identity
$$\Phi(s) = \sum_{n=1}^\infty \frac{\mu(n) (\log n)^k}{n^s} \sum_{r \in R(n)} \zeta(s,r/n) = \sum_{n=1}^\infty \frac{\Lambda_k'(f(n))}{n^s}$$
$$R(n) = \left\...

**5**

votes

**0**answers

104 views

### Gradient estimate for Poisson equation on manifold

In Gilbarg-Trudinger's book 'Elliptic Partial Differential Equations of Second order', the maximum principle is used to derive the following gradient estimates for Poisson equations on Euclidean ...

**2**

votes

**0**answers

103 views

### Long exact sequence from a short exact sequence of double complexes

I'm having trouble finding a reference for something that I think should be in the literature. Consider a short exact sequence of bounded double-complexes, in an abelian category:
$$0 \rightarrow A^{\...

**2**

votes

**0**answers

107 views

### Representation as $n=p^2+q^2-r^2$

What is known about the number of representations of a positive integer $n$ as
$$
\rho(n) = \# \{ (p,q,r): n=p^2+q^2-r^2\},
$$
where all the variables are primes?
What about the average number of ...