Find the residue of $frac{zeta'(1+s)}{zeta(1+s)}frac{x^s}{s}$ at $s=0$
$begingroup$
Let, $displaystyle f(s)=frac{zeta'(1+s)}{zeta(1+s)}frac{x^s}{s}$. Prove that $Res(f,s=0)=A-log x$ , for some constant $A$.
At $s=0$ , $zeta(s)$ has a pole of order $1$ and $zeta'(s)$ has a pole of order $2$. So, $frac{zeta'(1+s)}{zeta(1+s)}$ has a simple pole at $s=0$. Again , $x^s/s$ has a simple pole at $s=0$. So $f$ has a pole of order $2$ at $s=0$. So the residue is given by
$$lim_{sto 0}frac{d}{ds}left{sx^s.frac{zeta'(1+s)}{zeta(1+s)}right}.$$
I've stuck here ! How can I calculate this to prove the result ?
complex-analysis riemann-zeta zeta-functions
$endgroup$
add a comment |
$begingroup$
Let, $displaystyle f(s)=frac{zeta'(1+s)}{zeta(1+s)}frac{x^s}{s}$. Prove that $Res(f,s=0)=A-log x$ , for some constant $A$.
At $s=0$ , $zeta(s)$ has a pole of order $1$ and $zeta'(s)$ has a pole of order $2$. So, $frac{zeta'(1+s)}{zeta(1+s)}$ has a simple pole at $s=0$. Again , $x^s/s$ has a simple pole at $s=0$. So $f$ has a pole of order $2$ at $s=0$. So the residue is given by
$$lim_{sto 0}frac{d}{ds}left{sx^s.frac{zeta'(1+s)}{zeta(1+s)}right}.$$
I've stuck here ! How can I calculate this to prove the result ?
complex-analysis riemann-zeta zeta-functions
$endgroup$
1
$begingroup$
Hint: The answer should be that A is Euler–Mascheroni constant here.
$endgroup$
– Nanayajitzuki
Dec 9 '18 at 8:06
$begingroup$
$frac{x^s}{s} = frac{1}{s}+log x+O(s)$, do the same with $zeta'/zeta(1+s)$ and pick the coef of $1/s$ (which appears when integrating $int_{|s|=epsilon}$)
$endgroup$
– reuns
Dec 9 '18 at 8:09
add a comment |
$begingroup$
Let, $displaystyle f(s)=frac{zeta'(1+s)}{zeta(1+s)}frac{x^s}{s}$. Prove that $Res(f,s=0)=A-log x$ , for some constant $A$.
At $s=0$ , $zeta(s)$ has a pole of order $1$ and $zeta'(s)$ has a pole of order $2$. So, $frac{zeta'(1+s)}{zeta(1+s)}$ has a simple pole at $s=0$. Again , $x^s/s$ has a simple pole at $s=0$. So $f$ has a pole of order $2$ at $s=0$. So the residue is given by
$$lim_{sto 0}frac{d}{ds}left{sx^s.frac{zeta'(1+s)}{zeta(1+s)}right}.$$
I've stuck here ! How can I calculate this to prove the result ?
complex-analysis riemann-zeta zeta-functions
$endgroup$
Let, $displaystyle f(s)=frac{zeta'(1+s)}{zeta(1+s)}frac{x^s}{s}$. Prove that $Res(f,s=0)=A-log x$ , for some constant $A$.
At $s=0$ , $zeta(s)$ has a pole of order $1$ and $zeta'(s)$ has a pole of order $2$. So, $frac{zeta'(1+s)}{zeta(1+s)}$ has a simple pole at $s=0$. Again , $x^s/s$ has a simple pole at $s=0$. So $f$ has a pole of order $2$ at $s=0$. So the residue is given by
$$lim_{sto 0}frac{d}{ds}left{sx^s.frac{zeta'(1+s)}{zeta(1+s)}right}.$$
I've stuck here ! How can I calculate this to prove the result ?
complex-analysis riemann-zeta zeta-functions
complex-analysis riemann-zeta zeta-functions
asked Dec 9 '18 at 7:30
TopoTopo
323314
323314
1
$begingroup$
Hint: The answer should be that A is Euler–Mascheroni constant here.
$endgroup$
– Nanayajitzuki
Dec 9 '18 at 8:06
$begingroup$
$frac{x^s}{s} = frac{1}{s}+log x+O(s)$, do the same with $zeta'/zeta(1+s)$ and pick the coef of $1/s$ (which appears when integrating $int_{|s|=epsilon}$)
$endgroup$
– reuns
Dec 9 '18 at 8:09
add a comment |
1
$begingroup$
Hint: The answer should be that A is Euler–Mascheroni constant here.
$endgroup$
– Nanayajitzuki
Dec 9 '18 at 8:06
$begingroup$
$frac{x^s}{s} = frac{1}{s}+log x+O(s)$, do the same with $zeta'/zeta(1+s)$ and pick the coef of $1/s$ (which appears when integrating $int_{|s|=epsilon}$)
$endgroup$
– reuns
Dec 9 '18 at 8:09
1
1
$begingroup$
Hint: The answer should be that A is Euler–Mascheroni constant here.
$endgroup$
– Nanayajitzuki
Dec 9 '18 at 8:06
$begingroup$
Hint: The answer should be that A is Euler–Mascheroni constant here.
$endgroup$
– Nanayajitzuki
Dec 9 '18 at 8:06
$begingroup$
$frac{x^s}{s} = frac{1}{s}+log x+O(s)$, do the same with $zeta'/zeta(1+s)$ and pick the coef of $1/s$ (which appears when integrating $int_{|s|=epsilon}$)
$endgroup$
– reuns
Dec 9 '18 at 8:09
$begingroup$
$frac{x^s}{s} = frac{1}{s}+log x+O(s)$, do the same with $zeta'/zeta(1+s)$ and pick the coef of $1/s$ (which appears when integrating $int_{|s|=epsilon}$)
$endgroup$
– reuns
Dec 9 '18 at 8:09
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
You could get an easy access to answer if you already know the Stieltjes constants which appears in the Laurent series expansion of $zeta(s)$
$$displaystyle zeta (s)={frac{1}{s-1}}+sum _{n=0}^{infty}{frac{(-1)^{n}}{n!}}gamma _{n}(s-1)^{n}$$
and you take the first and constant item
$$displaystyle zeta (s+1)={frac{1}{s}}+gamma_{0}+O(s)$$
then you can find
$$displaystyle begin{align}
frac{zeta'(1+s)}{zeta(1+s)}&=frac{dln(zeta(1+s))}{ds}\&=frac{d}{ds}left(ln(1+gamma_{0}s+O(s^2))-ln sright)=frac{d}{ds}left(gamma_{0}s+O(s^2)-ln sright)\&={-frac{1}{s}}+gamma_{0}+O(s)
end{align}$$
notice you have
$$displaystyle frac{x^s}{s}=frac{1}{s}+ln x+O(s)$$
so you can easily get
$$displaystyle f(s)=-frac{1}{s^2}+frac{gamma_{0}-ln x}{s}+O(1)$$
here $gamma_{0}$ is Euler–Mascheroni constant, and the simply proof on the constant appears in the series can see another question like this one.
$endgroup$
add a comment |
$begingroup$
Due to the integral representation for the $zeta$ function, in a neighbourhood of $s=0$ we have
$$ zeta(s+1)=frac{1}{s}+gamma+(gamma_1+o(1))s = frac{1}{s}left[1+gamma s+O(1)sright]tag{1} $$
hence by applying $frac{d}{ds}log(cdot)$ to both sides
$$ frac{zeta'(s+1)}{zeta(s+1)} = -frac{1}{s}+gamma+O(1)s tag{2} $$
while
$$ frac{x^s}{s} = frac{1}{s}exp(slog x)=frac{1}{s}+log x+O(1)slog^2(x)tag{3}$$
hence by multiplying $(2)$ and $(3)$ we get that $s=0$ is a double pole of $frac{zeta'(s+1)}{zeta(s+1)}cdotfrac{x^s}{s}$ with residue $gamma-log x$.
$endgroup$
add a comment |
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2 Answers
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active
oldest
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2 Answers
2
active
oldest
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$begingroup$
You could get an easy access to answer if you already know the Stieltjes constants which appears in the Laurent series expansion of $zeta(s)$
$$displaystyle zeta (s)={frac{1}{s-1}}+sum _{n=0}^{infty}{frac{(-1)^{n}}{n!}}gamma _{n}(s-1)^{n}$$
and you take the first and constant item
$$displaystyle zeta (s+1)={frac{1}{s}}+gamma_{0}+O(s)$$
then you can find
$$displaystyle begin{align}
frac{zeta'(1+s)}{zeta(1+s)}&=frac{dln(zeta(1+s))}{ds}\&=frac{d}{ds}left(ln(1+gamma_{0}s+O(s^2))-ln sright)=frac{d}{ds}left(gamma_{0}s+O(s^2)-ln sright)\&={-frac{1}{s}}+gamma_{0}+O(s)
end{align}$$
notice you have
$$displaystyle frac{x^s}{s}=frac{1}{s}+ln x+O(s)$$
so you can easily get
$$displaystyle f(s)=-frac{1}{s^2}+frac{gamma_{0}-ln x}{s}+O(1)$$
here $gamma_{0}$ is Euler–Mascheroni constant, and the simply proof on the constant appears in the series can see another question like this one.
$endgroup$
add a comment |
$begingroup$
You could get an easy access to answer if you already know the Stieltjes constants which appears in the Laurent series expansion of $zeta(s)$
$$displaystyle zeta (s)={frac{1}{s-1}}+sum _{n=0}^{infty}{frac{(-1)^{n}}{n!}}gamma _{n}(s-1)^{n}$$
and you take the first and constant item
$$displaystyle zeta (s+1)={frac{1}{s}}+gamma_{0}+O(s)$$
then you can find
$$displaystyle begin{align}
frac{zeta'(1+s)}{zeta(1+s)}&=frac{dln(zeta(1+s))}{ds}\&=frac{d}{ds}left(ln(1+gamma_{0}s+O(s^2))-ln sright)=frac{d}{ds}left(gamma_{0}s+O(s^2)-ln sright)\&={-frac{1}{s}}+gamma_{0}+O(s)
end{align}$$
notice you have
$$displaystyle frac{x^s}{s}=frac{1}{s}+ln x+O(s)$$
so you can easily get
$$displaystyle f(s)=-frac{1}{s^2}+frac{gamma_{0}-ln x}{s}+O(1)$$
here $gamma_{0}$ is Euler–Mascheroni constant, and the simply proof on the constant appears in the series can see another question like this one.
$endgroup$
add a comment |
$begingroup$
You could get an easy access to answer if you already know the Stieltjes constants which appears in the Laurent series expansion of $zeta(s)$
$$displaystyle zeta (s)={frac{1}{s-1}}+sum _{n=0}^{infty}{frac{(-1)^{n}}{n!}}gamma _{n}(s-1)^{n}$$
and you take the first and constant item
$$displaystyle zeta (s+1)={frac{1}{s}}+gamma_{0}+O(s)$$
then you can find
$$displaystyle begin{align}
frac{zeta'(1+s)}{zeta(1+s)}&=frac{dln(zeta(1+s))}{ds}\&=frac{d}{ds}left(ln(1+gamma_{0}s+O(s^2))-ln sright)=frac{d}{ds}left(gamma_{0}s+O(s^2)-ln sright)\&={-frac{1}{s}}+gamma_{0}+O(s)
end{align}$$
notice you have
$$displaystyle frac{x^s}{s}=frac{1}{s}+ln x+O(s)$$
so you can easily get
$$displaystyle f(s)=-frac{1}{s^2}+frac{gamma_{0}-ln x}{s}+O(1)$$
here $gamma_{0}$ is Euler–Mascheroni constant, and the simply proof on the constant appears in the series can see another question like this one.
$endgroup$
You could get an easy access to answer if you already know the Stieltjes constants which appears in the Laurent series expansion of $zeta(s)$
$$displaystyle zeta (s)={frac{1}{s-1}}+sum _{n=0}^{infty}{frac{(-1)^{n}}{n!}}gamma _{n}(s-1)^{n}$$
and you take the first and constant item
$$displaystyle zeta (s+1)={frac{1}{s}}+gamma_{0}+O(s)$$
then you can find
$$displaystyle begin{align}
frac{zeta'(1+s)}{zeta(1+s)}&=frac{dln(zeta(1+s))}{ds}\&=frac{d}{ds}left(ln(1+gamma_{0}s+O(s^2))-ln sright)=frac{d}{ds}left(gamma_{0}s+O(s^2)-ln sright)\&={-frac{1}{s}}+gamma_{0}+O(s)
end{align}$$
notice you have
$$displaystyle frac{x^s}{s}=frac{1}{s}+ln x+O(s)$$
so you can easily get
$$displaystyle f(s)=-frac{1}{s^2}+frac{gamma_{0}-ln x}{s}+O(1)$$
here $gamma_{0}$ is Euler–Mascheroni constant, and the simply proof on the constant appears in the series can see another question like this one.
edited Dec 9 '18 at 11:48
answered Dec 9 '18 at 11:40
NanayajitzukiNanayajitzuki
3185
3185
add a comment |
add a comment |
$begingroup$
Due to the integral representation for the $zeta$ function, in a neighbourhood of $s=0$ we have
$$ zeta(s+1)=frac{1}{s}+gamma+(gamma_1+o(1))s = frac{1}{s}left[1+gamma s+O(1)sright]tag{1} $$
hence by applying $frac{d}{ds}log(cdot)$ to both sides
$$ frac{zeta'(s+1)}{zeta(s+1)} = -frac{1}{s}+gamma+O(1)s tag{2} $$
while
$$ frac{x^s}{s} = frac{1}{s}exp(slog x)=frac{1}{s}+log x+O(1)slog^2(x)tag{3}$$
hence by multiplying $(2)$ and $(3)$ we get that $s=0$ is a double pole of $frac{zeta'(s+1)}{zeta(s+1)}cdotfrac{x^s}{s}$ with residue $gamma-log x$.
$endgroup$
add a comment |
$begingroup$
Due to the integral representation for the $zeta$ function, in a neighbourhood of $s=0$ we have
$$ zeta(s+1)=frac{1}{s}+gamma+(gamma_1+o(1))s = frac{1}{s}left[1+gamma s+O(1)sright]tag{1} $$
hence by applying $frac{d}{ds}log(cdot)$ to both sides
$$ frac{zeta'(s+1)}{zeta(s+1)} = -frac{1}{s}+gamma+O(1)s tag{2} $$
while
$$ frac{x^s}{s} = frac{1}{s}exp(slog x)=frac{1}{s}+log x+O(1)slog^2(x)tag{3}$$
hence by multiplying $(2)$ and $(3)$ we get that $s=0$ is a double pole of $frac{zeta'(s+1)}{zeta(s+1)}cdotfrac{x^s}{s}$ with residue $gamma-log x$.
$endgroup$
add a comment |
$begingroup$
Due to the integral representation for the $zeta$ function, in a neighbourhood of $s=0$ we have
$$ zeta(s+1)=frac{1}{s}+gamma+(gamma_1+o(1))s = frac{1}{s}left[1+gamma s+O(1)sright]tag{1} $$
hence by applying $frac{d}{ds}log(cdot)$ to both sides
$$ frac{zeta'(s+1)}{zeta(s+1)} = -frac{1}{s}+gamma+O(1)s tag{2} $$
while
$$ frac{x^s}{s} = frac{1}{s}exp(slog x)=frac{1}{s}+log x+O(1)slog^2(x)tag{3}$$
hence by multiplying $(2)$ and $(3)$ we get that $s=0$ is a double pole of $frac{zeta'(s+1)}{zeta(s+1)}cdotfrac{x^s}{s}$ with residue $gamma-log x$.
$endgroup$
Due to the integral representation for the $zeta$ function, in a neighbourhood of $s=0$ we have
$$ zeta(s+1)=frac{1}{s}+gamma+(gamma_1+o(1))s = frac{1}{s}left[1+gamma s+O(1)sright]tag{1} $$
hence by applying $frac{d}{ds}log(cdot)$ to both sides
$$ frac{zeta'(s+1)}{zeta(s+1)} = -frac{1}{s}+gamma+O(1)s tag{2} $$
while
$$ frac{x^s}{s} = frac{1}{s}exp(slog x)=frac{1}{s}+log x+O(1)slog^2(x)tag{3}$$
hence by multiplying $(2)$ and $(3)$ we get that $s=0$ is a double pole of $frac{zeta'(s+1)}{zeta(s+1)}cdotfrac{x^s}{s}$ with residue $gamma-log x$.
answered Dec 9 '18 at 11:31
Jack D'AurizioJack D'Aurizio
289k33282662
289k33282662
add a comment |
add a comment |
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1
$begingroup$
Hint: The answer should be that A is Euler–Mascheroni constant here.
$endgroup$
– Nanayajitzuki
Dec 9 '18 at 8:06
$begingroup$
$frac{x^s}{s} = frac{1}{s}+log x+O(s)$, do the same with $zeta'/zeta(1+s)$ and pick the coef of $1/s$ (which appears when integrating $int_{|s|=epsilon}$)
$endgroup$
– reuns
Dec 9 '18 at 8:09