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**3**

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**0**answers

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### Where does Aphex Twin's “windowlicker” equation come from? [closed]

$\Delta M_i^{-1} = -\alpha \sum\limits_{n=1}^N D_i [n] \left[\sum\limits_{j \in C[i]} F_{ji} [n-1] + Fext_i [n^{-1}]\right]$
This is the name of the second song on Aphex Twin's album "Windowlicker". ...

**9**

votes

**3**answers

885 views

### Spaces with a quasi triangle inequality

How do you call a space with a function which is symmetric, non negative, positive definite and which satisfies a quasi-triangle inequality:
$d(x,z) \leq C( d(x,y)+d(y,z) )$
for all $x,y,z$ and some ...

**13**

votes

**3**answers

955 views

### Card game / options pricing / Brownian bridge question

We play a game. I shuffle a deck of cards and start dealing them face up. After any card you can say "stop", at which point I pay you 1 dollar for every red card dealt and you pay me 1 for every black ...

**14**

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**12**answers

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### Why semigroups could be important?

There is known a lot about the use of groups -- they just really appear a lot, and appear naturally. Is there any known nice use of semigroups in Maths to sort of prove they are indeed important in ...

**7**

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**2**answers

906 views

### Are there uncountably many essentially inequivalent versions of Mathematics?

Hi everyone,
Disclaimer 1: logic and set theory are a long way from my field, so apologies in advance if I demonstrate extreme ignorance or stupidity, and please correct me if (when?) I write stupid ...

**1**

vote

**0**answers

280 views

### Why semigroups are important? [closed]

There is known a lot about semigroups, mostly about their inner structure etc. But is there any use of semigroups in the general Maths -- like that of groups?

**1**

vote

**1**answer

455 views

### Is there a conjunction bias?

This is slightly related to question The unprecedented success of the “intersection” operator .
Apart from a set of maths books of null measure, most have the following property:
Objects ...

**2**

votes

**2**answers

1k views

### Advice on Giving a Talk [closed]

What advice do you have for giving a talk on a mathematical research paper to people in other fields in science (not physics nor astronomy) but without lot of math background?
Thanks.

**4**

votes

**1**answer

2k views

### Who is this guy : Z.A. Melzak (wrote Companion to Concrete Mathematics) ? [closed]

Author : Z.A. Melzak
Book Title : Companion to Concrete Mathematics.
Publication : Dover renewed 2004 2 volumes in one. Copyright 1972/1976.
I found this book extremely nice.
To whet your appetite ...

**4**

votes

**3**answers

631 views

### Is the componentwise square-root of a positive-definite matrix also pos.-def.?

Let $A=(a_{ij}) \in \mathbb{R}^{n \times n}$ be a matrix with $a_{ij} = a_{ji} \geq 0$ and
$B=(b_{ij})$ with $b_{ij} = \sqrt{a_{ij}}$.
Is $B$ positive-definite whenever $A$ is?
In other words:
...

**-1**

votes

**1**answer

1k views

### Unpopular “elementary” theorems/identities to impress an audience of mathematicians. [closed]

This question grew out of my recent job interview. Since the interviewers were math professors, I had a hard time searching for interesting elementary theorems in case I got asked for one.
I thought ...

**80**

votes

**90**answers

11k views

### What would you want to see at the Museum of Mathematics?

EDIT (30 Nov 2012): MoMath is opening in a couple of weeks, so this seems like it might be a good time for any last-minute additions to this question before I vote to close my own question as "no ...

**7**

votes

**1**answer

1k views

### Technical trends quietly aimed at big open problems? [closed]

When I was an undergraduate 35 years ago, I made the mistake of asking some of my mathematics professors what well-known open problems they liked to think about. I got the message that this was ...

**12**

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**17**answers

2k views

### Individual mathematical objects whose study amounts to a (sub)discipline? [closed]

Certain mathematical objects have a theory so rich that their study
alone arguably constitutes a distinct (sub)discipline. My own list
would begin with
1) the absolute Galois group of the rationals;
...

**1**

vote

**0**answers

165 views

### Regarding a Feature of Multivariate Real Function

Any real function can be expressed as a function of the sum of two monotonic real functions?
More precisely, for real function p(x, y), there exist continuous real functions P(x), h(x,y), g(x) such ...

**1**

vote

**0**answers

528 views

### What is the name for(a^2 + b^2 + c^2 +…)/(a + b + c +…)? [closed]

That is, the sum of squares of some numbers divided by the sum of the numbers. The term "anti-harmonic mean" has been coined for this quantity. I'm hoping there is a better name.

**47**

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**6**answers

6k views

### Still Difficult After All These Years

I think we all secretly hope that in the long run mathematics becomes easier, in that with advances of perspective, today's difficult results will seem easier to future mathematicians. If I were ...

**53**

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**26**answers

5k views

### Proof synopsis collection

I hate to keep going with the big lists, but the question about one-sentence summaries of topics/areas spurred this question...and I just can't help myself!
Definition (Fraleigh): A proof synopsis ...

**14**

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**35**answers

2k views

### Basic results with three or more hypotheses

Consider the following statement of the Arzela-Ascoli theorem.
Theorem. Let K be a compact topological space and let S be a subset of C(K). Then S is relatively compact if and only if S is uniformly ...

**13**

votes

**2**answers

829 views

### Is there a name for sets for which it is easier to test membership than to find members---and vice versa?

This is a question my son Bob asked me. For some sets it is relatively easy
to test for membership but a lot more difficult to find members, and for others
the reverse is true. Here is an elementary ...

**3**

votes

**4**answers

3k views

### Theorems true but wrong. [closed]

Many theorems have the form : Premise(es) implies Conclusion(s)
Example A of wrongness:
There are many examples in which a theorem is stated without mentioning that part of the premise is not ...

**43**

votes

**6**answers

5k views

### Does a referee have to check carefully the proof ?

I have always checked very carefully the papers I was refereeing when I wanted to suggest "accept". Actually I spend almost as much time checking the maths of a paper I referee than checking the maths ...

**30**

votes

**6**answers

4k views

### Why is the Gaussian so pervasive in mathematics?

This is a heuristic question that I think was once asked by Serge Lang. The gaussian: $e^{-x^2}$ appears as the fixed point to the Fourier transform, in the punchline to the central limit theorem, as ...

**1**

vote

**2**answers

840 views

### Example of a function that behaves like another function

I need a function $f(x)$ with the following properties -
It should be monotonically non-decreasing.
For $x \geq 1$, $x + \frac{1}{x} - f(x) < \epsilon$ where $\epsilon$ is an extremely small ...

**7**

votes

**3**answers

573 views

### What is the strategy for “all words valid” scrabble?

The rules for "all words valid" scrabble are exactly the same as ordinary scrabble, except that every single combination of letters is in the dictionary. To make the game deterministic, we will also ...

**2**

votes

**3**answers

741 views

### Is there a simple criterion to determine if two parallelograms intersect?

see title.
assume we are given two parallelograms in the plane. how can I check if the intersection is nonempty?
note that I do not need to actually find the intersection.

**116**

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**36**answers

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### Demonstrating that rigour is important

Any pure mathematician will from time to time discuss, or think about, the question of why we care about proofs, or to put the question in a more precise form, why we seem to be so much happier with ...

**5**

votes

**1**answer

496 views

### Elementary problem about triangles inside a convex polygon

Let P be a convex polygon with area A(P), and to each side of P, attach the largest area triangle possible that lies entirely within P. Must the sum S(P) of the areas of these triangles always satisfy ...

**7**

votes

**1**answer

593 views

### Sum of subset of geometric series: a^2^n

The formula for 1 + a + a^2 + .... where 0 < a < 1 is $\frac{1}{1-a}$, but what if you wanted to sum only those where the exponent is a power of 2? That is,
$S = a + a^2 + a^4 + a^8 + \cdots$
...

**2**

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**7**answers

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### Books about polynomials [closed]

Hi,have you a good reference (books) for the study of polynomials with one variable or many variables ? Thanks for your help.
Don't hesitate to correct my English.