Questions tagged [polygamma]
For questions about, or related to the polygamma function.
0
votes
1answer
28 views
Derivative of polygamma function
I am working on my Matlab homework and I have to make a derivative of function $f(x)=\psi (x)\cdot \sin (x)$ , where $\psi(x)$ is polygamma function. What the derivative of $\psi(x)$ will be?
1
vote
0answers
34 views
Digamma function question
I just learned online about Polygamma functions, and I want to know what $x$ equals (and how to get it) when $\psi(x)=1$ and $x>1$.
0
votes
1answer
27 views
Dimensional regularization and expansion of gamma function
In my calculations, I used dimensional regularization, i.e. replace $d\rightarrow d-\epsilon$ and calculated the divergent integral. Then, I would like to expand the answer into seriers by $\epsilon$ ...
5
votes
2answers
171 views
Seeking methods to solve: $\int_0^\infty \frac{\ln(t)}{t^n + 1}\:dt$
Seeking Methods to solve the following two definite integrals:
\begin{equation}
I_(n) = \int_0^\infty \frac{\ln(t)}{t^n + 1}\:dt \qquad J(n) = \int_0^\infty \frac{\ln^2(t)}{t^n + 1}\:dt
\end{equation}...
1
vote
0answers
48 views
How to show: $\psi^{(0)}\left(\frac{1}{n}\right) - \psi^{(0)}\left(1 - \frac{1}{n}\right) = -\pi\cot\left(\frac{\pi}{n}\right)$ [duplicate]
Based on a result I found recently and in conjunction with methods I've observed on MSE I was able to show that:
\begin{equation}
\int_0^\infty \frac{ \ln(t)}{t^n + 1}\:dt = -\frac{\pi^2}{n^2} \...
3
votes
2answers
122 views
Alternative proof for $\zeta\left(2,\frac14\right)=\psi^{(1)}\left(\frac14\right)=\pi^2+8G$
On the German Wikipedia page of the Hurwitz Zeta Function I have come across the following formula
$$\zeta\left(2,\frac14\right)~=~\pi^2+8G\tag1$$
Where $G$ is Catalan's Constant. Even though I ...
1
vote
1answer
39 views
Polygamma expression for $\frac{\Gamma^{(k)}(z)}{\Gamma(z)}$?
I'm trying to simplify
$$\frac{\Gamma^{(k)}(z)}{\Gamma(z)}$$
for $k=1,2,\cdots$, using polygamma notation
Try
I've calculated a few, using
$$\Gamma^{(k)}(z) = \int_0^\infty (\log x)^k x^{z-1} ...
2
votes
1answer
137 views
Is it possible to simplify $\psi^{(2)}(\frac18)$ or $\psi^{(2)}(\frac pq)$?
Is it possible to simplify $\psi^{(2)}(\frac18)$, where $\psi$ denotes the polygamma function?
Or more generalized, $\psi^{(2)}(\frac pq)$ and $\psi^{(2n)}(\frac pq)$?
Background
Noticing there is ...
1
vote
1answer
46 views
Is the polygamma function of order $2$ non-negative (or negative) for all $x >0$?
The polygamma function of order $2$ is defined as
$$\psi^{(2)}(z)= \frac{d^2}{dz^2} \psi(z) = \frac{d^{3}}{dz^{3}} \ln\Gamma(z)$$
where $\Gamma(z)$ is the usual gamma function: $\int_0^\infty x^{z-1}...
5
votes
1answer
136 views
On the series expansion of $\frac{\operatorname{Li}_3(-x)}{1+x}$ and its usage
Recently I have asked about the evaluation of an integral involving a Trilogarithm $($which can be found here$)$. Pisco provided a quite elegant approach starting with a functional equation of the ...
0
votes
1answer
133 views
$\sum_{n=1}^{4000000} \frac{1}{n^3}$ very quick.
Some days ago I have tried to find the sum of the first milion terms of the infinite sum $\zeta(3) = \sum_{n=1}^\infty\frac{1}{n^3}$ (Apéry's constant) on Wolfram Programming Lab (Open Cloud), an ...
0
votes
1answer
53 views
Logarithmic Sum
Is there a closed form for the following sum? $$\sum_{n=0}^{\infty}\sum_{m=1}^{\infty}(-1)^{m+n}\frac{\ln(m+n)}{(m+n)}$$
According to https://www.mathmash.org/contestprob.php?prob=227 it has a closed ...
2
votes
2answers
163 views
Relation between harmonic series $H(m)$ and polygamma function?
I have the following formula:
$$h(x)=\sum_{R=1}^m \frac{1}{R+1}-1$$
I have re-expressed this (correctly, I hope!) in terms of the harmonic number $H(m)=\sum_{R=1}^m \frac{1}{R}$:
$$h(x)=H(m)+\frac{...
0
votes
1answer
68 views
The meaning and definition of $\psi^{(-2)}(x)$, and the convergence of some related series involving the Möbius function
While I was playing with a CAS I find that makes sense the function $$\psi^{(-k)}(x),$$
for example $\psi^{(-2)}(x)$, where $\psi^{(n)}(x)$ denotes the $n$th derivative of the digamma function, see ...
0
votes
1answer
221 views
Series Representation of Gamma Function
The $\Gamma(x)$ is function That has derivatives in the polygamma form.
Can those derivatives be used to make a Taylor series? I've tried but I got stuck as soon as I find out That $\Psi^1(1)=\zeta(2)=...
2
votes
0answers
57 views
Generalized hypergeometric function at unity
I wonder if there is a closed formula for the following generalized hypergeometric function at $z=1$:
$${}_4F_3\left(a,a,a,a;a+1,a+1,2a;1\right)$$
Specifically, I would like to have a formula in ...
0
votes
1answer
110 views
Evaluate an infinite series involving the polygamma function OR first derivative of the hurwitz zeta function
Can we find a closed form for
$$\sum _{k=1}^\infty\frac{\left(-1\right)^k}{2k-1}\left(2k^2-k+8k^2P_1(k)-16kP_2(k)+16P_3(k)\right)$$
where
$$P_n(k)=\psi^{(-n)}\left(k+\frac12\right)-\psi^{(-n)}\left(k+...
0
votes
1answer
32 views
Explicit forms of negapolygamma difference with arguments that differ by a half?
There are well known explicit formulas for negapolygamma expressions of the form
$$\psi^{(-n)}(x)-\psi^{(-n)}(x-1)$$
for $n\in\mathbb{N}\gt1$
for example
$$\psi^{(-2)}\left(x\right)-\psi^{(-2)}\left(...
1
vote
2answers
60 views
I ran $\frac{d^n}{dx^n}[(x!)!]$ through the calculator but don’t understand the $R^{(0,1)}$ and $R(n,x)$ in the output
I ran $\frac{d^n}{dx^n}[(x!)!]$ through Wolfram|Alpha, which returned
$$\frac{\partial^n(x!)!}{\partial x^n} = \Gamma(1+x!)\,R(n,1+x!)$$
for
$R(n,x)=\psi(x)\,R(-1+n,x)+R^{(0,1)}(-1+n,x)$
...
0
votes
1answer
89 views
Recurrence relation for the polygamma function of negative order?
I know the recurrence relation for the Polygamma function is
$$\psi^{(m)}(x+1)=\psi^{(m)}(x)+\frac{(-1)^mm!}{x^{m+1}}$$
Does such a recurrence formula exist for negative integer $m$?
I am using the ...
0
votes
1answer
204 views
Are the real and imaginary parts of Riemann zeta equal to each other by multiplication of a Riemann Siegel theta function expression?
It appears that the real part of Riemann zeta is related to the imaginary part by this formula:
$$\Re\left(\zeta \left(\frac{1}{2}+i t\right)\right)=\frac{\Im\left(\zeta \left(\frac{1}{2}+i t\right)\...
6
votes
1answer
178 views
Evaluating $\psi^{(1/2)}(x)$ of the extended polygamma function
The polygamma function is generally given by
$$\psi^{(n)}(x)=\frac{d^{n+1}}{dx^{n+1}}\ln(\Gamma(x)),~n\in\mathbb N_{\ge0}$$
where $\Gamma$ is the gamma function. This can be extended to negative ...
1
vote
0answers
67 views
Infinite Gamma Derivative Identity
We have
$$
\Gamma(z)=\int_0^\infty x^{z-1}e^{-x}\;dx \tag{1}
$$
We also have
$$
\frac{d^n}{dz^n}\, x^{z-1}e^{-x}=\log(x)^n e^{-x}x^{z-1}, \;\; z>1 \tag{2}
$$
If we create an operator
$$
\hat{O}=\...
2
votes
1answer
315 views
Poles of hypergeometric function $_2F_1$
We consider the hypergeometric function $ _2F_1 [\dfrac{1}{2}(1+k+l+\omega), \dfrac{1}{2}(1+k-l+\omega), 1+k, -r^2]$, and use its expansion as given in [1] in terms of the rising Pochhammer symbols. ...
0
votes
0answers
24 views
How to sum this vaguely zeta-looking function to QGammafunctions?
For
$q>1$
and
$s\ge{}1$,
I'm trying to express
$$\sum_{n=1}^\infty \dfrac{1}{(1-q^n)^s}$$
in terms of the Qpolygamma function.
Just from its definition, it's clear to see that for $s$ the ...
2
votes
2answers
338 views
Asymptotic expansion of Polygamma functions
According to Wikipedia, the log-Gamma and Polygamma functions have the following asymptotic behaviour on the real line for $x\to\infty$:
$$\ln\Gamma(x) = (x - \tfrac{1}{2}) \ln(x) - x + \tfrac{1}{2}\...
5
votes
2answers
197 views
Asymptotic behavior of Harmonic-like series $\sum_{n=1}^{k} \psi(n) \psi'(n) - (\ln k)^2/2$ as $k \to \infty$
I would like to obtain a closed form for the following limit:
$$I_2=\lim_{k\to \infty} \left ( - (\ln k)^2/2 +\sum_{n=1}^{k} \psi(n) \, \psi'(n) \right)$$
Here $\psi(n)$ is digamma function.
Using ...
-1
votes
1answer
515 views
Solve the system of equations in the maximum likelihood estimation of Gamma distribution parameters
I'm trying to calculate the two parameters of the Gamma distribution by solving the system of two equations obtained by differentiating the ...
2
votes
1answer
57 views
Path containing zeros of all derivatives
Following @mercio's comments, I've rewritten my question in terms of zeros instead of saddles. Also, after more careful consideration, I've decided that perhaps the path I seek might not depend on the ...
1
vote
0answers
103 views
Convexity of reciprocal polygamma
Is the reciprocal of polygamma functions of odd order convex on $ \mathbb{R^+}$, while that of even order above 0 concave? Plotting the functions suggest so, but I've been trying for days to come up ...
5
votes
0answers
120 views
Closed form for $\sum_{k\geq 1}\frac{1}{(2^k-1)^a}$
Is there a closed form for
$$f(a)=\sum_{k=1}^\infty\frac{1}{(2^k-1)^a},$$
where $0<a\in\mathbb{R}$.
My attempts so far have considered $a\in\mathbb{N}$, which appears to give finite sums of the q-...
0
votes
0answers
61 views
Does the following digamma/trigamma inequality hold? And can it be formally shown?
Suppose $x > \frac{1}{2}$. Let $\psi^{(0)}$ and $\psi^{(1)}$ denote the digamma and trigamma functions, respectively. Does the following inequality hold for any such $x$?
$\psi^{(0)}(x) - \psi^{(0)...
2
votes
1answer
72 views
Prove or disprove: Is $\psi(x) - \psi(x + y)$ an increasing function of $x > 0$, for all $y > 0$?
The title says it all. Let $y$ be a fixed positive real value. For any such $y$, is $\psi(x) - \psi(x + y)$ an increasing function of $x > 0$?
Here $\psi(x)$ is the digamma function, defined by:
$...
2
votes
0answers
91 views
Relation between the derivative of hurwitz zeta and trigamma
How to prove that
$$\zeta '(-1, 1/3)- \zeta '(-1, 2/3) = \frac{\psi ' (1/3)}{6 \sqrt{3} \pi}-\frac{\pi}{9 \sqrt{3}}$$
Does there exist a general formula for
$$\zeta '(-1, x)- \zeta '(-1, 1-x) $$
0
votes
1answer
87 views
On $\lim_{x\to 0}\frac{-(1+\sqrt{-x})\psi^{(0)}(1-\sqrt{-x})+(1+\sqrt{-x})\psi^{(0)}(\sqrt{-x}+1)+2\psi^{(0)}(1+x)}{2(\sqrt{-x}-1)(\sqrt{-x}+1)x}$
I've copy the identity in my Question from the solution of Wolfram Alpha online calculator. The expression is tedious to write thus I hope that there are no typos. When you type the code
sum 1/((k+...
1
vote
1answer
363 views
Show some properties of the Digamma Function
Let $\psi(z)$ denote the Digamma function, $\psi(z)=\frac{d}{dz}\ln \Gamma(z)=\frac{\Gamma'(z)}{\Gamma(z)}$. I am meant to show the following properties of $\psi$:
$\psi$ is meromorphic in $\mathbb{C}...
9
votes
2answers
382 views
Integral $\int_0^\infty\Big[\log\left(1+x^2\right)-\psi\left(1+x^2\right)\Big]dx$
I found this intriguing integral:
$$\int_0^\infty\Big[\log\left(1+x^2\right)-\psi\left(1+x^2\right)\Big]dx\approx0.84767315533332877726581...$$
where $\psi(z)=\partial_z\log\Gamma(z)$ is the digamma.
...
2
votes
1answer
156 views
Closed Form for the Integral: $\int_0^1 t^n\log\Gamma(t+a)dt$
I am wondering if someone could tell me whether or not the following integral has a closed form representation:
$$\int_0^1 t^n\log\Gamma(t+a)dt$$
In Srivastava's and Choi's wonderful book Zeta and q-...
1
vote
0answers
66 views
Does this reduce down to the PolyGamma function?
Does this reduce down to the PolyGamma function?
$H_n=$
$$\lim_{s\to 0} \, \left(-\frac{\left(\frac{1}{s}+1\right)^n (s+1)^{-n} \left(\sum _{k=0}^{\infty } \frac{\left(-\frac{1}{s}\right)^k \left(\...
14
votes
1answer
474 views
Closed form for $\sum_{n=0}^\infty\frac{\Gamma\left(n+\tfrac14\right)}{2^n\,(4n+1)^2\,n!}$
I was experimenting with hypergeometric-like series and discovered the following conjecture (so far confirmed by more than $5000$ decimal digits):
$$\sum_{n=0}^\infty\frac{\Gamma\!\left(n+\tfrac14\...
2
votes
1answer
135 views
Minimizing $f(x)=A^{\frac{tx-1}{x-1}} \left( c^x \frac{\Gamma(0.5+x)}{\sqrt{\pi}} \right)^{\frac{1-t}{x-1}}$ subject to the constraint
Let $f(r)$ be a function defined as follows
\begin{align}
f(x)=A^{\frac{tx-1}{x-1}} \left( c^x \frac{\Gamma(0.5+x)}{\sqrt{\pi}} \right)^{\frac{1-t}{x-1}}
\end{align}
where $0 < A,c$ and $ t\in (0,...
7
votes
1answer
189 views
Closed form for $\sum_{n=1}^{\infty} \frac{1}{1+n+n^2+\cdots+n^a}$
Does anyone know if there happens to exist a closed form solution for this sum:
$$\sum_{n=1}^{\infty} \frac{1}{1+n+n^2+\cdots+n^a}$$
For low values of $a$, Wolfram Alpha gives a closed form in terms ...
16
votes
2answers
572 views
Conjectured closed form for $\operatorname{Li}_2\!\left(\sqrt{2-\sqrt3}\cdot e^{i\pi/12}\right)$
There are few known closed form for values of the dilogarithm at specific points. Sometimes only the real part or only the imaginary part of the value is known, or a relation between several different ...
24
votes
2answers
724 views
Integral ${\large\int}_0^1\ln^3\!\left(1+x+x^2\right)dx$
I'm interested in this integral:
$$I=\int_0^1\ln^3\!\left(1+x+x^2\right)dx.\tag1$$
Can we prove that
$$\begin{align}I&\stackrel{\color{gray}?}=\frac32\ln^33-9\ln^23+36\ln3+2\pi^2\ln3-\frac{4\pi^2}...
13
votes
2answers
492 views
Conjecture $\int_0^1\frac{\ln^2\left(1+x+x^2\right)}x dx\stackrel?=\frac{2\pi}{9\sqrt3}\psi^{(1)}(\tfrac13)-\frac{4\pi^3}{27\sqrt3}-\frac23\zeta(3)$
I'm interested in the following definite integral:
$$I=\int_0^1\frac{\ln^2\!\left(1+x+x^2\right)}x\,dx.\tag1$$
The corresponding antiderivative can be evaluated with Mathematica, but even after ...
10
votes
0answers
214 views
Asymptotic behavior of the generalized polygamma function
The generalized polygamma function$^{[1]}$$\!^{[2]}$ is defined as
$$\psi^{(\nu)}(z)=e^{-\gamma\!\;\nu}\;\partial_\nu\!\left(\frac{e^{\gamma\!\;\nu}\;\zeta(\nu+1,z)}{\Gamma(-\nu)}\right),\tag1$$
where ...
2
votes
1answer
249 views
Re-Expressing the Digamma
I was reading some articles on the digamma function, and I was wondering if anyone knows how to express the digamma function $\psi^{(0)}(n)$ in terms of a trigonometric function or a logarithmic ...
2
votes
1answer
85 views
Logarithmic Integral I
Consider the integral
\begin{align}
I = \int_{0}^{1} \frac{ \ln^{2}x}{(x^{2} - x + 1)^{2}} \, dx.
\end{align}
It is speculated that the value is
\begin{align}
I = \frac{10 \, \pi^{3}}{3^{5} \, \sqrt{3}...
2
votes
1answer
114 views
Bounding infinite series derived from polygamma functions
Let $f(x) = 2 \psi^{(1)}(x+1) + x \psi^{(2)}(x+1) $
for $ x > 0 $, where $\psi^{(i)}(x)$ is the $i^{th}$ derivative of the
digamma function $\psi(x)$.
The goal is to prove that $ f(x) < \frac{...
0
votes
1answer
52 views
Solve for X in the given Equation(Gamma Curve)
I'm having a set of points in the form:
${(\frac A{255})}^{\frac 1x}=\frac B{255}$
I need to Find $x$ in the Equation.Where $A$ & $B$ are set of constants ranging from $0$ to $255$. Please ...
