# Questions tagged [quasimodular-forms]

The quasimodular-forms tag has no usage guidance.

13
questions

4
votes

0
answers

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### Logarithmic vector-valued modular functions and quasimodular forms with misleading modular weights

I have a somewhat imprecise question about functions with reasonably nice modular transformations that don't seem to fit nicely into what I understand of the plain vanilla theory of modular and ...

2
votes

0
answers

127
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### theta function with a low bound in the sum

I encounter a sum similar to the Jacobi Theta function except there is a lower bound $-J$ with $J\geq 0$:
\begin{equation}
f(q,x)=\sum_{n=-J}^\infty q^{n^2}x^n.
\end{equation}
My question is whether ...

13
votes

2
answers

1k
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### Complex Multiplication and algebraic integers

Let $q=e^{2\pi i\tau}$ and
$$E_2(\tau) = 1 - 24 \sum_{n=1}^\infty\frac{nq^n}{1-q^n}$$ be the Eisenstein Series of weight $2$
and let $E_2^*(\tau) = E_2(\tau) - \frac{3}{\pi\cdot Im(\tau)}$ be the ...

6
votes

1
answer

534
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### How to compute Coefficients in Chudnovsky's Formula?

My aim is to understand all three coefficients arising in the Chudnovsky-Formula (see also Question 300385). Two of them are easily computed, but I failed with the third:
It is known that for all $\...

21
votes

1
answer

1k
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### Why does this quasi-modular function have integral values?

It is a well-known result that the modular function $1728J(\tau) := \frac{1728E_4(\tau)^3}{E_4(\tau)^3-E_6(\tau)^2}$ has integral values if $\tau$ has class number 1 - for example at $\tau_{163}:=\...

16
votes

0
answers

381
views

### Power series which are $p$-adic modular forms for all $p$

Suppose that, for some integer $k$, a series $f(q) \in \mathbb Q \otimes \mathbb Z[[q]]$ has the property that for every prime $p$, $f(q)$ is the $q$-expansion of a $p$-adic modular form of weight $k$ ...

4
votes

1
answer

738
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### Algebraic independence of $E_2$, $E_4$ and $E_6$

In "M. Kaneko and D. Zagier, A generalized Jacobi theta function and quasimodular forms, Prog. Math. 129,
165-172 (1995)" there is a proposition stating essentially that $E_2$, $E_4$ and $E_6$ are ...

1
vote

1
answer

270
views

### $f,f',...,f^{(j)}$ is $\mathbb C$-linearly independent if $f$ is a modular form

Conjecture: Let be $f$ a modular form of weight $k$ and $j$ a strictly positive integer, then the set $f,f',...,f^{(j)}$ is $\mathbb C$-linearly independent in $A$.
Is that conjecture true or false? ...

7
votes

1
answer

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### How do the rings of level $N$ quasi-modular forms related to the rings of modular forms?

It is well known that the graded algebra $\mathcal{M}(1)$ of Modular forms for $\Gamma = PSL_2(\mathbb{Z})$ is the polynomial algebra
$$
\mathcal{M}(1) = \mathbb{C}[E_4, E_6]
$$
where $E_4$ and $E_6$ ...

10
votes

2
answers

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### Binomial coefficients and derivatives of modular forms

Let $E_2$, $E_4$, and $E_6$ denote the standard Eisenstein series.
The usual variables $q=e^{2\pi i\tau}$ allow us to regard the
$E_n$'s as functions on either the upper half plane or the unit
disk ...

4
votes

2
answers

779
views

### What literature is known about MacMahon's generalized sum-of-divisors function?

MacMahon in the paper Divisors of Numbers and their Continuations in the Theory of Partitions defines several generalized notions of the sum-of-divisors function; for example, if we write $a_{n,k}$ ...

16
votes

3
answers

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### How do modular forms of half-integral weight relate to the (quasi-modular) Eisenstein series?

The Eisenstein series
$$
G_{2k} = \sum_{(m,n) \neq (0,0)} \frac{1}{(m + n\tau)^{2k}}
$$
are modular forms (if $k>1$) of weight $2k$ and quasi-modular if $k=1$. It is clear that given modular forms $...

13
votes

2
answers

937
views

### Modular equations for quasimodular forms

This problem is motivated by this question and by teaching
modular polynomials for the classical modular invariant $j(\tau)$.
The latter implies
that if we consider the fields of modular functions $\...