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Real-valued functions of real variable, analytic properties of functions and sequences, limits, continuity, smoothness of these.

2 votes

How can we obtain the $-\frac{4\pi}3\mu(x)$ term?

This is just a further detalization of the Carlo Beenakker's answer. Let us write $$K_{ik}=\int\left (\frac{\partial^2}{\partial r_i \partial r_k}\frac{1}{r}\right )\mu(\vec{y})d\vec{y},$$ where $r_i= …
Zurab Silagadze's user avatar
14 votes
Accepted

On an example of an eventually oscillating function

In addition to Noam Elkies and David Speyer's answers. "Harder" explanation is made somewhat "softer" in http://www.maths.bris.ac.uk/~majpk/papers/37.pdf (Summability of alternating gap series, by J. …
Zurab Silagadze's user avatar
3 votes

Introductory texts to mathematics

I would recommend Mathematical Omnibus: Thirty Lectures on Classic Mathematics, by D. B. Fuks and Serge Tabachnikov: http://books.google.ru/books?id=bomkJMq2H9sC&source=gbs_similarbooks and also books …
22 votes
3 answers
2k views

The origin of the Ramanujan's $\pi^4\approx 2143/22$ identity

What is the origin of the Ramanujan's approximate identity $$\pi^4\approx 2143/22,\;\;\tag 1$$ which is valid with $10^{-9}$ relative accuracy? For comparison, the relative accuracy of the well known …
Zurab Silagadze's user avatar
4 votes
Accepted

"Values" of divergent integrals

For an attempt of such a theory, see http://carlossicoli.free.fr/B/Burgin_M.-Hypernumbers_and_Extrafunctions__Extending_the_Classical_Calculus-Springer(2012).pdf (Hypernumbers and Extrafunctions: Exte …
Zurab Silagadze's user avatar
4 votes

Numerically computing $\int_0^1 \frac{1}{\sqrt{1-x^4}}dx$

How Gauss (supposedly) calculated this integral in terms of AGM (namely $M(1,\sqrt{2})$) is outlined in http://home.sandiego.edu/~langton/gaussagm.pdf (Gauss, recurrence relations, and the AGM, by Sta …
Zurab Silagadze's user avatar
21 votes
0 answers
651 views

A multiple integral

Let us consider the multiple integral $$I_{n}=\int_{-\infty }^{\infty }ds_{1}\int_{-\infty}^{s_{1}}ds_{2}\cdots \int_{-\infty }^{s_{2n-1}}ds_{2n}\;\cos {(s_{1}^{2}-s_{2}^{2})}\;\cdots \cos {(s_{2n-1 …
Zurab Silagadze's user avatar
2 votes

Stokes theorem with corners

This book http://www.math.wustl.edu/~sk/books/root.pdf (Geometric Integration Theory, by S.G. Krantz and H.R. Parks) is a self-contained introduction to geometric measure theory. See also Hassler Whit …
Zurab Silagadze's user avatar
1 vote

Quantum Mechanics and bilinear optimal control theory

In addition to the literature indicated by Carlo Beenakker: in this 2015 review http://arxiv.org/abs/1508.00442 (Training Schrödinger's cat: quantum optimal control, by S.J. Glaser et al.) the authors …
Zurab Silagadze's user avatar