# Questions tagged [closed-form-expressions]

For questions that specifically ask for determining a closed form of equations, integrals etc.

142
questions

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71 views

### Closed form for $\sum _{k=1} ^n \frac k 2 \,\operatorname{sgn} \left( \frac 1 {k^2} + \cos \frac {2\pi n} k-1 \right)$

I am looking for the closed form of
$$\sum _{k=1} ^n \frac k 2 \,\operatorname{sgn} \left( \frac 1 {k^2} + \cos \frac {2\pi n} k-1 \right) \ .$$
Wolfram Alpha cannot do this for me, so I am forced to ...

**0**

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**0**answers

19 views

### Closed-form expression for the integral of a Gamma CDF times a Rice PDF

Given the following CDF and PDF
\begin{equation}
{F_{\gamma_d}}(\gamma_d)=Q\left(\kappa ,0,\sqrt{\frac{{\lambda_d}}{\theta ^2}}\right)~~\text{for $\gamma_d>0$} ,
\end{equation}
\begin{equation}
...

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21 views

### Reduction of the general Lauricella hypergeometric function $F_B$ for identical parameters and variables

The Lauricella function $F_B^{n}$ of $n$ variables is defined as $$F_B^{(n)}(a_1, \ldots, a_n, b_1, \ldots, b_n, c; x_1, \ldots x_n) = \sum_{k_1, \ldots, k_n = 0}^\infty \frac{1}{(c)_{k_1 + \ldots + ...

**0**

votes

**1**answer

159 views

### Where is the source of the formula $\sum_{j=0}^\infty \bigl(j+\frac{1}{2}\bigr)^{n-1}\frac{2^{j+1/2}}{\binom{2j+1}{j+1/2}}$ for an integer sequence?

The infinite series representation
\begin{equation}
\frac1\pi\sum_{j=0}^\infty \biggl(j+\frac{1}{2}\biggr)^{n-1}\frac{2^{j+1/2}}{\binom{2j+1}{j+1/2}}, \quad n\ge0
\end{equation}
for the positive ...

**2**

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**0**answers

206 views

### Is there a closed form of $ \displaystyle \sum_{k=0}^{\infty}{\frac{\phi^{xk}}{k!_F}}$

where $\phi = \frac{1+\sqrt{5}}{2}$ and $k!_F$ is the fibonorial of $k$, or the product of the first $k$ Fibonacci numbers? My hunch is that, this can be represented as a function in terms of the ...

**1**

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138 views

### How to explicitly obtain an analytic function whose power series coefficients are sums over integer compositions?

Starting with the following differential equation,
\begin{eqnarray}
x \frac{\partial^3}{\partial x^3} P[h, x] - \frac{\partial^2}{\partial h^2} \left( h \frac{\partial}{\partial h} P [h, x] \right) ...

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76 views

### Any known relations to this doubly exponential constant?

Two years back I was working with lacunary series. In my explorations I had derived that the following series is periodic with period 1:
$$ f(x)= \sum_{n=0}^{\infty} \left[ e^{2^{x+n}} \right] + x - \...

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25 views

### Solution to dynamic program-type recursion

I have the following dynamic programming principle-type problem.
Suppose that we are given a sequence $\beta_1,\dots,\beta_n\in (0,\infty)$, some target $y\in (0,\infty)$ with $y>\sum_{t=1}^N \...

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**0**answers

82 views

### How to determine the closed form of this Fourier series?

Consider the Series
$$
S(z) \equiv \sum_{n \in \mathbb{Z}, n \ne 0} \frac{ 1 }{ \sin n\pi \tau \sin 2n \pi \tau } e^{2\pi i n z} \ , \quad \operatorname{Im}\tau > 0
$$
I am trying to find its ...

**1**

vote

**1**answer

159 views

### Generalizing closed form representations related to conjectured analytic formulas for $f_a(x)=\sum\limits_{n=1}^x a(n)$

Consider the summatory function $f_a(x)$ defined in formula (1) below where the related Dirichlet series $F_a(s)$ defined in formula (2) below converges for $\Re(s)\ge 2$.
$$f_a(x)=\sum\limits_{n=1}^...

**0**

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77 views

### Requesting proof of closed form of sum involving Fibonacci and Lucas numbers

$$ \sum_{n=0}^{k+1}\frac{3F_{n+1}-L_{n+1}}{2n!}\frac{(k+1)!}{(k-n+1)!}x^{k-n+1}=(\varphi+x)^k\left(\frac{\sqrt{5}}{5}-\frac{\sqrt{5}-5}{10}x\right)+(\psi+x)^k\left(\frac{\sqrt{5}+5}{10}x-\frac{\sqrt{5}...

**2**

votes

**1**answer

245 views

### Closed form of $\prod_{k=1}^{n}\left(\cos(kx)-1\right)$

Is there any closed form of
$$\prod_{k=1}^{n}\left(\cos(kx)-1\right)?$$
I failed to find references on this problem in the internet.

**3**

votes

**2**answers

308 views

### About the integral $\int_{0}^{1}\frac{\log(x)}{\sqrt{1+x^{4}}}dx$ and elliptic functions

NOTE: I post this question on math.stackexchange but nobody answered, so I try here.
For a work we need to evaluate the following integral $$\int_{0}^{1}\frac{\log\left(x\right)}{\sqrt{1+x^{4}}}dx=\,-...

**3**

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**0**answers

188 views

### Spherical harmonic expansion of a power function

Let $f$ be an even continuous function on the sphere $S^{n-1}$.
Find a relation of the spherical harmonic expansion between coefficients of $f^n$ and those of $f$.

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78 views

### Expression for the single common root

Let $ \mathbb{F} $ be a field, consider the polynomial ring $ \mathbb{F} \left[ x\right] $ and suppose that the polynomials $f,g \in \mathbb{F} \left[ x\right]$ have degrees $2,2^n$, respectively, ...

**3**

votes

**1**answer

51 views

### General formula for the integral w.r.t to Marchenko-Pastur density, of the ratio of degree $\le 2$ polynomials

Question. Is there a closed-form formula (via standard objects like rational functions, radicals, special functions, special numbers like Catalan numbers, etc.) expressing integrals of rational ...

**0**

votes

**2**answers

243 views

### Closed form for $\sum_{i=1}^n{a^{i^2}}$

Let $a$ be an element of some ring or field, possibly finite.
Is there closed form for $\sum_{i=1}^n{a^{i^2}}$?
sage and wolframalpha couldn't solve it.
If $a$ is primitive n-th root of unity this is ...

**5**

votes

**4**answers

323 views

### Is this closed-form summation a special case of known Lerch zeta function formulas?

With some Poisson summation manipulations (credit: Michał Pacholski) I have convinced myself of a closed form expression for this conditionally convergent series:
$$\sum_{n=-\infty}^\infty \frac{e^{in\...

**7**

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**0**answers

250 views

### Closed form of the sum $\sum_{r\ge2}\frac{\zeta(r)}{r^2}$

Note: This question has been brought here from MSE.
I have been working on various sums involving the zeta function (which come up frequently in my research), and it turned out that many of them had ...

**0**

votes

**1**answer

73 views

### Closed-form for recursive "geometric-like" recursion

I asked this question of MSE, but to no avail; alas, here I am.
Let $k>0$, $C\geq 1$, $\alpha \in (0,1]$, and let $(x_n)_{n\geq 1}$, be a sequence of real numbers given by the recursion
$$
x_{n+1} =...

**1**

vote

**1**answer

113 views

### An ambitiouser binomial coefficients sum

I asked how to calculate $$\sum_{i = 0}^b(-1)^i\binom{b}{i}\binom{a+b-i-1}{a-i}$$ and got amazing answers. A bit later, however, I figured I needed something rather more complicated: I need to find ...

**-1**

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**3**answers

194 views

### Binomial Coefficients sum [closed]

Any idea on whether or not $$\sum_{i = 0}^b(-1)^i\binom{b}{i}\binom{a+b-i-1}{a-i}$$
has a closed formula on $a$ and $b$ (and on what it is, in case it does)?
It is supposed that $b \le a$.

**6**

votes

**2**answers

323 views

### Closed form for $\sum_{j=0}^{\infty}{\alpha \choose j} {\beta \choose j}x^j$

As stated, I wonder if there is a closed form for the generating function $F_{\alpha,\beta}(x):=\sum_{j=0}^{\infty}{\alpha \choose j} {\beta \choose j}x^j$ where $\alpha,\beta \in\mathbb{N}$. Calling ...

**2**

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**0**answers

85 views

### How to solve a QCQP where constraints are balls?

I want to solve the following optimization problem in variables $\theta_1, \theta_2, \dots, \theta_K$
\begin{equation}
\begin{aligned}
& \underset{\theta}{\text{minimize}}
& & \...

**7**

votes

**3**answers

316 views

### Invertibility of specific function

This is my first post. I'm not a mathematician, just an electronics engineer who loves mathematics. In one of my projects, I arrived at the following function:
$$V\left(\varphi\right)=\frac{A\sqrt{\pi-...

**6**

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**0**answers

108 views

### Fourier transformation of a distribution

We have no idea how to tackle the following Fourier transformation of a distribution:
$$
\lim_{\epsilon\to0^+}\int_{-\infty}^{\infty}\mathrm{d} t\int_{\mathbb{R}^{d-1}} \mathrm{d}^{d-1}\vec{r} e^{-\...

**1**

vote

**1**answer

186 views

### Analytically controlling sizes in modular arithmetic to demonstrate Dirichlet pigeonhole application

Given $a,b,c,d\in\mathbb Z$ with $ad+bc=p$ a prime there is an $m\in\mathbb Z$ with $-\lceil1+\sqrt{p}\rceil<
r_1,r_2<\lceil1+\sqrt{p}\rceil$ and
$$r_1\equiv mac\bmod p$$
$$r_2\equiv mbd\bmod p$$...

**4**

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**0**answers

158 views

### Can $ x \sum_{k=1}^{\infty} \frac{1}{k} \Big{(}- \gamma - \psi \big{(}1-\frac{x}{k} \big{)} \Big{)} $ be simplified?

I'm interested in sums of the form $$f_{p} (x) = \sum_{k=2}^{\infty} \zeta(k)^{p} x^{k} .$$
For $p=1$, the following result is known: $$f_{1} (x) = -x \big{(}\psi(1-x) + \gamma \big{)} .$$
(That is, ...

**-2**

votes

**1**answer

199 views

### Is it possible to express $\int_{0+\epsilon}^{1-\epsilon}\left(\sqrt{1-x^2}^{\sqrt{1-x^2}^{\cdots}}\right) dx$ in elementary functions?

let $\epsilon >0$, I tried to evaluate $\int_{0+\epsilon}^{1-\epsilon}\left(\sqrt{1-x^2}^{\sqrt{1-x^2}^{\cdots}}\right) dx$ , using the fact $x= \cos t$ yield to have integrand using $\sin $ ...

**1**

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**0**answers

79 views

### Extension of closed-form solvability of polynomial equations of x and exp to rational expressions?

Is my conjecture below true?
It's a new conjecture. It's an extension of Lin's theorem in [Lin 1983] which is cited in [Chow 1999] - see both references at the bottom of this page.
It seems that Ferng-...

**4**

votes

**2**answers

369 views

### From Zurab's integral representation for the Apéry's constant to almost impossible integrals

I would like to know if the following integrals are known, or in case that aren't in the literature we can calculate these in closed-form (in terms of elementary and standard functions). I wondered ...

**7**

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**2**answers

467 views

### A second order nonlinear ODE

In my research (in differential geometry) I recently came across the following nonlinear second order ode:
$$\frac{f''(x)}{f'(x)}-\frac{2}{x}+\frac{f'(x)+1}{2f(x)-x-1}+\frac{f'(x)-1}{2f(x)+x}=0$$
It ...

**1**

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**0**answers

69 views

### Why do we not have a closed form expression for counting transitivity?

https://en.wikipedia.org/wiki/Transitive_relation.
Are there any theoretical reasons out there which show us that why do we still not have a closed-form expression for transitivity counting. If you ...

**1**

vote

**1**answer

489 views

### Find closed-form expression to $f(n)$

For all $n \in \mathbb{N}$, set
$f(n)=
\begin{cases}
\min_{a\in\{\lceil n/2\rceil, \lceil n/2\rceil+1,\dots, n-1\}} \frac 1 4 \binom n a f(a) & \text{if $n\geq 4$}\\
1 & \text{otherwise}
\...

**0**

votes

**1**answer

105 views

### PDF of $z = \exp(j\varphi)$, where $\varphi \sim \mathcal{U}[-a, +a]$ [closed]

How can I find the PDF of $z = \exp(j\varphi)$, where $\varphi \sim \mathcal{U}[-a, +a]$, $i.e.$, a uniformly distributed r.v.?
My difficulty here is that it involves complex numbers and I don't know ...

**2**

votes

**0**answers

84 views

### Closed form expression for this Fourier summation?

Consider the function $f:\mathbb{T}^m\to\mathbb{R}$
$$f(\boldsymbol{x}) = \sum\limits_{{\pmb{\eta}\in\mathbb{Z}^m}}\frac{1}{1+\lambda\|\pmb{\eta}\|_{2k}^{2k} } \cos({2\pi \pmb{\eta}\cdot\pmb{x}})$$
...

**1**

vote

**2**answers

296 views

### Closed form of $\prod_{i=0}^{N}\big(i!\big)^{{N}\choose{i}}$

I have made a question here about closed form of the following:
$$\prod_{k=0}^{N}\big(k!\big)^{{N}\choose{k}}$$
I know that there is a known closed form for,
$$\prod_{i=0}^{N}\big(i!\big)=G(N+2)$$
...

**4**

votes

**1**answer

313 views

### About $a_n = \frac{a_{n-1}(a_{n-1} + C)}{a_{n-2}}.$

Let $A,B,C > 0$. Put $a_1 = A$ and $a_2 = B$ and, for integer $n > 2$,
$$a_n = \frac{a_{n-1}(a_{n-1} + C)}{a_{n-2}}$$
and
$$ T = \lim_{k \to \infty} \frac{a_k}{ a_{k - 1}}.$$
Notice the limit ...

**11**

votes

**1**answer

384 views

### Closed Form for $\sum\limits_{n=-2a}^\infty(n+a){2a\choose-n}^4,~a\not\in\mathbb Z$

Do either $~S_4^+(a)~=~\displaystyle\sum_{n=0}^\infty(n+a){2a\choose n}^4~$ or $~S_4^-(a)~=~\displaystyle\sum_{n=-2a}^\infty(n+a){2a\choose-n}^4~$ possess a meaningful closed form expression1 in terms ...

**2**

votes

**2**answers

368 views

### PDF of $ | \sum_{k=1}^{n}{|h_k||g_k|\exp\left( j \theta_k \right)} |^2$ for small values of $n$ and $Q$?

Given the following function of random variables
$$f = \left|\sum_{k=1}^{n}{|h_k||g_k|\exp\left( j \theta_k \right)} \right|^2,$$
where $h_1, \cdots, h_n$ and $g_1, \cdots, h_n$ are i.i.d. random ...

**0**

votes

**2**answers

146 views

### PDF of $g = \frac{1}{n} \sum_{k=1}^{n}{|h_k|\exp\left( j \theta_k \right)}$?

Given the following function of random variables
$$g = \frac{1}{n} \sum_{k=1}^{n}{|h_k|\exp\left( j \theta_k \right)},$$
where $h_1, \cdots, h_n$ are i.i.d. random variables following the complex ...

**0**

votes

**2**answers

228 views

### PDF of $R$ given that $R^2 = C^2 + S^2$, with $C = \sum_{j=1}^{n}{\cos \theta_j}$ and $S = \sum_{j=1}^{n}{\sin \theta_j}$ for a small $n$

Suppose that $\theta_1, \cdots, \theta_n$ are distributed independently and that $\theta_j$ has probability density function (PDF) $f_j = \frac{1}{2\pi}$ ($i.e.$, the uniform distribution) for $j = 1, ...

**6**

votes

**0**answers

180 views

### A class of symmetric functions

When attacking a symmetric problem via an asymmetric method, I encountered the following function: $$U_2(n, m) = \sum_{a = 0}^n\binom na (2^a + 2^{n - a})^m.$$
It is easy to see that this function is ...

**0**

votes

**0**answers

76 views

### What is the closed-form solution to this double-sum norm function?

Given two points $A,B \in \mathbb{R}^2$, one defines the Euclidean distance $f: \mathbb{R}^2\times\mathbb{R}^2 \rightarrow \mathbb{R}^{\ge 0}$ as follows.
$$f(A,B) := \Vert A-B \Vert : = \sqrt{(A_{x}...

**2**

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**0**answers

169 views

### Proof of non-solvability of general equations of one unknown in elementary terms (finite terms)?

This question relates to the solvability of equations of one unknown in elementary terms (finite terms) according to Liouville and Ritt.
Elementary equations and closed-form solutions can be ...

**2**

votes

**0**answers

79 views

### Closed form for unusual recurrence

We have for $k>0$, $n>0$, $m\geqslant0$
$$p_k(n,m)=k(n-1)!\sum\limits_{s=0}^{n-1}\frac{p_{k-1}(s+1,m+1)+p_{k-1}(m+1,s)}{s!}$$
also
$$p_0(n,m)=\begin{cases}
(n-1)!,&\text{$n>0, m=0$}\\
0,&...

**1**

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**0**answers

447 views

### The mysterious numbers $ \frac{13}{20} $ and $20$?

Let $g(x) = x^6 - 30 x $
Let $h(x) = x^6 $
Let $f(x) = x^2 - 2 $
Let $r$ be a reduced fraction $0 < \frac{p}{q} < 2 $ with integers $p,q > 1$
Let $f_{n+1}(x) = f(f_n(x)) = f_n(f(x)) , ...

**5**

votes

**1**answer

488 views

### On the integral $\int_0^1\log(x!)dx$ revisited

I was interested in an integral that I known from [1], it is
$$\int_0^1 \log(x!)dx.$$
I tried to get such closed-form using myself ideas and symbolic calculations, also with the help of Wolfram ...

**1**

vote

**2**answers

68 views

### Expectation of $\left| \frac{(\textbf{x}+\textbf{y})^{H} \textbf{x} }{\| \textbf{x} + \textbf{y} \|^2} \right|^2$, with complex Gaussians?

Given that following two random variables $\textbf{x} \sim \mathcal{CN}(\textbf{0}_{M},\sigma_{x}^{2}\textbf{I}_{M})$ and $\textbf{y} \sim \mathcal{CN}(\textbf{0}_{M},\sigma_{y}^{2}\textbf{I}_{M})$ ...

**1**

vote

**1**answer

366 views

### On $\zeta(7)$ as the integration of the product of an indefinite integral due to Lobachevskii by a power of the inverse Gudermannian function

In this post I invoke certain function from a post of this site MathOverflow it is [1] (please see further references from the post, authors from the Springer link of the cited literature and answers ...