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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

2 votes

Questions about some parallel between polynomial and differential equation

The answer to Q2 is provided by Differential algebra created by Joseph Fels Ritt. He studied differential-algebraic varieties by analogy with algebraic ones. See Ritt, Joseph Fels, Differential algebr …
Alexandre Eremenko's user avatar
37 votes
Accepted

How did Riemann prove that the moduli space of compact Riemann surfaces of genus $g>1$ has d...

Riemann combines what is called Riemann-Roch and Riemann-Hurwitz nowadays. He considers the dimension of the space of holomorphic maps of degree $d$ from the Riemann surface of genus $g$ to the sphere …
Alexandre Eremenko's user avatar
14 votes
4 answers
2k views

Examples of plane algebraic curves

There are many interesting sequences of polynomials which contain polynomials of arbitrarily high degree, for example classical orthogonal polynomials. Most of them arise as characteristic polynomials …
3 votes

Quadrature of the Lune

This is indeed the theorem of Chebotarev and Dorodnov, the original articles are Tschebotaröw, Nikolaj Über quadrierbare Kreisbogenzweiecke. I. (German) Zbl 0010.00103. Math. Z. 39, 161-175 (1934). A. …
Alexandre Eremenko's user avatar
1 vote

Calculation of solid angle for rectangle in 6DOF

You can do this without integration, by performing the following steps. Calculate the coordinates of the vertices of your rectangle. Let the vertices be $v_1,v_2,v_3,v_4$. Let your point "source" be …
Alexandre Eremenko's user avatar
29 votes

Algebraic geometry over the complex numbers, and beyond

Algebraic geometry began over the field of reals. What Apollonius of Perga did would be certainly qualified today as algebraic geometry: he classified real plane curves of second order and studied the …
Alexandre Eremenko's user avatar
1 vote

Approaching the Riemann-Roch Theorem for algebraic curves

Several proofs are available. If you are interested in a short algebraic proof, I can recommend S. Lang, Introduction to algebraic and Abelian functions, Addison-Wesley, Reading, MA, 1972. First 25 pa …
Alexandre Eremenko's user avatar
3 votes

Explicit universal covering map for higher genus algebraic curves

The answer is no, except some very special cases. There is a comprehensive book dedicated to this: H. P. de Sain-Gervais, Uniformisation des surfaces de Riemann, ENS Ed., 2010. There is an English tra …
Alexandre Eremenko's user avatar
7 votes
Accepted

Constructing proper holomorphic self-mappings of the unit disk with a given set of branch po...

This (existence and uniqueness) is proved in the paper in much more general setting (in fact, the result is due to E. Picard): M. Heins, ‘On a class of conformal metrics’, Nagoya Math. J. 21 (1962) 1– …
Alexandre Eremenko's user avatar
5 votes

What are parabolic bundles good for?

They arise in analytic theory of differential equations with regular singularities, Riemann Hilbert problem and Painleve equations. MR1924757 Biswas, Indranil A criterion for the existence of a flat c …
Martin Sleziak's user avatar
4 votes

Can the theory of elliptic functions developed from purely geometric considerations?

Some elementary parts of the theory of elliptic functions can indeed be developed in this way. To those books listed by Alexey Ustinov I can add a large treatise by G. Halphen, Traité des fonctions el …
David Roberts's user avatar
  • 35.4k
32 votes

How would a topologist explain "every Riemann surface of genus $g$ is hyperelliptic if and o...

A 19th century topologist would explain this by dimension count. By Riemann-Hurwitz, a surface of genus $g$ covering the sphere with $2$ sheets has $2g+2$ ramification points which gives $2g-1$ free c …
GH from MO's user avatar
  • 105k
6 votes
Accepted

How can I show $\{\mathbf{x}: \dim (\ker M_1(\mathbf{x}) \cap \ker M_2(\mathbf{x})) \geq C \...

Evidently, $\mathrm{Ker} M_1\cap \mathrm{Ker} M_2=\mathrm{Ker}(M_1,M_2)$, where $(M_1,M_2)=:M$ is the $2m\times m$ matrix obtained by putting $M_1,M_2$ together ($k$-th column of $M$ consists the of t …
Alexandre Eremenko's user avatar
4 votes

Algebraic closure of $\mathbb{C}(t)$

Elements of $\overline{C(t)}$ are not really functions since they do not have a common domain that would allow to add and multiply them. One way to think of $\overline{C(t)}$ is to consider the field …
Alexandre Eremenko's user avatar
5 votes

What is the state-of-the-art for solving polynomials systems over fields that are not algebr...

For the real field: MR2830310 Sottile, Frank Real solutions to equations from geometry. University Lecture Series, 57. American Mathematical Society, Providence, RI, 2011. MR2275625 Mikhalkin, Grigo …
gmvh's user avatar
  • 3,065

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