Mathematics Stack Exchange
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Questions tagged [modular-forms]

A modular form is a (complex) analytic function on the upper half-plane satisfying a certain kind of functional equation with respect to the group action of the modular group.

In mathematics, a modular form is a (complex) analytic function on the upper half-plane satisfying a certain kind of functional equation with respect to the group action of the modular group, and also satisfying a growth condition. The theory of modular forms therefore belongs to complex analysis but the main importance of the theory has traditionally been in its connections with number theory. Modular forms appear in other areas, such as algebraic topology and string theory (Wikipedia).

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Proof of $\frac{1}{e^{\pi}+1}+\frac{3}{e^{3\pi}+1}+\frac{5}{e^{5\pi}+1}+\ldots=\frac{1}{24}$

I would like to prove that $\displaystyle\sum_{\substack{n=1\\n\text{ odd}}}^{\infty}\frac{n}{e^{n\pi}+1}=\frac1{24}$. I found a solution by myself 10 hours after I posted it, here it is: $$f(x)=\sum_{\substack{n=1\\n\text{…
danodare
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Intuition for the Importance of Modular Forms

I am learning about modular forms for the first time this term and am just starting to wrap my head around what might be the big picture of things. I was wondering if the following interpretation of why modular forms are important is correct a)…
Alex Youcis
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Evaluate $\int_{-\infty}^\infty\frac{x}{\sin^2(\sqrt{x})\sinh^2\left(2\sqrt{2x}\right)+\pi^2\cos^2(\sqrt{x})\cosh^2\left(2\sqrt{2x}\right)}\mathrm dx$

I encountered an astonishing integral (numerically verified): $$\int_{-\infty}^\infty \frac{x\ \mathrm dx}{\sin ^2(\sqrt{x}) \sinh ^2(2 \sqrt{2 x})+\pi ^2 \cos ^2(\sqrt{x}) \cosh ^2(2 \sqrt{2 x})}\\ \small =-\frac{1}{262144 \pi ^3}\left(18…
Infiniticism
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Other interesting consequences of $d=163$?

Question: Any other interesting consequences of $d=163$ having class number $h(-d)=1$ aside from the list below? Let $\tau = \tfrac{1+\sqrt{-163}}{2}$. We have (see notes at end of list), $$e^{\pi\sqrt{163}}\approx…
Tito Piezas III
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Demystifying modular forms

I am really struggling to understand what modular forms are and how I should think of them. Unfortunately I often see others being in the same shoes as me when it comes to modular forms, I imagine because the amount of background knowledge needed to…
user929304
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In what sense is Taniyama-Shimura the $n=2$ case of Langlands?

As I understand it (If I'm imprecise, as I will likely be, please correct me), Langlands says roughly as follows: For every representation $Gal(\mathbb{Q}) \rightarrow GL_n(\mathbb{C})$ we can form a function, called the associated…
Nicole
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How does one see Hecke Operators as helping to generalize Quadratic Reciprocity?

My question is really about how to think of Hecke operators as helping to generalize quadratic reciprocity. Quadratic reciprocity can be stated like this: Let $\rho: Gal(\mathbb{Q})\rightarrow GL_1(\mathbb{C})$ be a $1$-dimensional representation…
Nicole
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How does Wiles' proof fail at $n=2$?

The content is miles outside what I know about. So the question is a mixture of idle curiosity and maybe having this answered somewhere on the Internet. It is likely I will not be able to understand the answer. How exactly does Wiles' proof of…
JP McCarthy
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The importance of modular forms

I'm studying modular forms and my professor started the course talking about elliptic functions. These particular functions form a field (once that the lattice $\Lambda$ is fixed) called $E(\Lambda)=\mathbb C(\wp,\wp')$ and they "represent" all…
Dubious
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Deligne, elliptic curves and modular forms

I'm trying to understand an argument of Deligne (in Courbes elliptiques: Formulaire d'après J. Tate), but I'm not familiar enough with algebraic geometry, so I'm getting quite confused. So even in my statement I might say things that don't make any…
Nadim Rustom
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What is the exact value of $\eta(6i)$?

Let $\eta(\tau)$ be the Dedekind eta function. In his Lost Notebook, Ramanujan played around with a related function and came up with some of the nice evaluations, $$\begin{aligned} \eta(i) &= \frac{1}{2}…
Tito Piezas III
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Why are $L$-functions a big deal?

I've been studying modular forms this semester and we did a lot of calculations of $L$-functions, e.g. $L$-functions of Dirichlet-characters and $L$-functions of cusp-forms. But I somehow don't see, why they are considered a big deal. To me it…
Steven
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On the integral $\int_0^\infty \eta^2(i x) \,dx = \ln(1+\sqrt{3}+\sqrt{3+2 \sqrt{3}})$ and its cousins

While experimenting with integrals involving the Dedekind Eta function, I came across a family of integrals which seem to follow a very simple pattern. With $y \in \mathbb{N}$, define: $$A(y) = \int_0^{\infty} \eta( i x)\,\eta(i x y)\,dx.$$ The…
Noam Shalev - nospoon
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a new continued fraction for $\sqrt{2}$

In a q-continued fraction related to the octahedral group I defined a new q-continued fraction for the square of ramanujan's octic continued fraction which I discovered using certain three term relations and algebraic manipulations. Given…
Nicco
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When does a modular form satisfy a differential equation with rational coefficients?

Given a modular form $f$ of weight $k$ for a congruence subgroup $\Gamma$, and a modular function $t$ for $\Gamma$ with $t(i\infty)=0$, we can form a function $F$ such that $F(t(z))=f(z)$ (at least locally), and we know that this $F$ must now…
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