Big Oh of values of Riemann zeta function












-1












$begingroup$


There is a equality in a proof in Apostol's Analytic Number Theory as follows:
$O(x^{alpha} zeta(alpha)) = O(x^{alpha})$ for arbitrary real number $alpha ge 0$.



How do we say that? Does anything changes when $alpha in [0,1]$?










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$endgroup$








  • 1




    $begingroup$
    It is not correct. Check out $zeta(1)$ for $alpha=1$, e.g., here. What section/chapter is this in Apostol?
    $endgroup$
    – Dietrich Burde
    Jan 17 at 20:12












  • $begingroup$
    It is in Chapter 3, Theorem 3.5.
    $endgroup$
    – Ninja
    Jan 18 at 10:45










  • $begingroup$
    My bad, $alpha$ is any positive number except $1$. What happens now?
    $endgroup$
    – Ninja
    Jan 18 at 10:46
















-1












$begingroup$


There is a equality in a proof in Apostol's Analytic Number Theory as follows:
$O(x^{alpha} zeta(alpha)) = O(x^{alpha})$ for arbitrary real number $alpha ge 0$.



How do we say that? Does anything changes when $alpha in [0,1]$?










share|cite|improve this question









$endgroup$








  • 1




    $begingroup$
    It is not correct. Check out $zeta(1)$ for $alpha=1$, e.g., here. What section/chapter is this in Apostol?
    $endgroup$
    – Dietrich Burde
    Jan 17 at 20:12












  • $begingroup$
    It is in Chapter 3, Theorem 3.5.
    $endgroup$
    – Ninja
    Jan 18 at 10:45










  • $begingroup$
    My bad, $alpha$ is any positive number except $1$. What happens now?
    $endgroup$
    – Ninja
    Jan 18 at 10:46














-1












-1








-1





$begingroup$


There is a equality in a proof in Apostol's Analytic Number Theory as follows:
$O(x^{alpha} zeta(alpha)) = O(x^{alpha})$ for arbitrary real number $alpha ge 0$.



How do we say that? Does anything changes when $alpha in [0,1]$?










share|cite|improve this question









$endgroup$




There is a equality in a proof in Apostol's Analytic Number Theory as follows:
$O(x^{alpha} zeta(alpha)) = O(x^{alpha})$ for arbitrary real number $alpha ge 0$.



How do we say that? Does anything changes when $alpha in [0,1]$?







number-theory analytic-number-theory riemann-zeta






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share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Jan 17 at 20:09









NinjaNinja

1,105720




1,105720








  • 1




    $begingroup$
    It is not correct. Check out $zeta(1)$ for $alpha=1$, e.g., here. What section/chapter is this in Apostol?
    $endgroup$
    – Dietrich Burde
    Jan 17 at 20:12












  • $begingroup$
    It is in Chapter 3, Theorem 3.5.
    $endgroup$
    – Ninja
    Jan 18 at 10:45










  • $begingroup$
    My bad, $alpha$ is any positive number except $1$. What happens now?
    $endgroup$
    – Ninja
    Jan 18 at 10:46














  • 1




    $begingroup$
    It is not correct. Check out $zeta(1)$ for $alpha=1$, e.g., here. What section/chapter is this in Apostol?
    $endgroup$
    – Dietrich Burde
    Jan 17 at 20:12












  • $begingroup$
    It is in Chapter 3, Theorem 3.5.
    $endgroup$
    – Ninja
    Jan 18 at 10:45










  • $begingroup$
    My bad, $alpha$ is any positive number except $1$. What happens now?
    $endgroup$
    – Ninja
    Jan 18 at 10:46








1




1




$begingroup$
It is not correct. Check out $zeta(1)$ for $alpha=1$, e.g., here. What section/chapter is this in Apostol?
$endgroup$
– Dietrich Burde
Jan 17 at 20:12






$begingroup$
It is not correct. Check out $zeta(1)$ for $alpha=1$, e.g., here. What section/chapter is this in Apostol?
$endgroup$
– Dietrich Burde
Jan 17 at 20:12














$begingroup$
It is in Chapter 3, Theorem 3.5.
$endgroup$
– Ninja
Jan 18 at 10:45




$begingroup$
It is in Chapter 3, Theorem 3.5.
$endgroup$
– Ninja
Jan 18 at 10:45












$begingroup$
My bad, $alpha$ is any positive number except $1$. What happens now?
$endgroup$
– Ninja
Jan 18 at 10:46




$begingroup$
My bad, $alpha$ is any positive number except $1$. What happens now?
$endgroup$
– Ninja
Jan 18 at 10:46










1 Answer
1






active

oldest

votes


















0












$begingroup$

The thing is - as far as the implied limit there is concerned - for fixed $alpha$ as $x$ varies, $zeta(alpha)$ is just a number. $O(cf(x))=O(f(x))$ for any constant $c$ and function $f$.



As noted in the comments, $alpha=1$ is an exception; there, $O(x^{alpha}zeta(alpha))$ becomes $O(infty)$, which is vacuously true for any function of $x$.



In practice, the places you'll actually want to use this always come from values of $alpha$ for which the series for $zeta$ converges - namely, $alpha>1$. However, it's still true for $alpha<1$, using the definitionof $zeta$ by analytic continuation.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    OK, $alpha=1$ is special. $O(infty)$ is a rather meaningless proposition.
    $endgroup$
    – jmerry
    Jan 17 at 21:47











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1 Answer
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active

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1 Answer
1






active

oldest

votes









active

oldest

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active

oldest

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0












$begingroup$

The thing is - as far as the implied limit there is concerned - for fixed $alpha$ as $x$ varies, $zeta(alpha)$ is just a number. $O(cf(x))=O(f(x))$ for any constant $c$ and function $f$.



As noted in the comments, $alpha=1$ is an exception; there, $O(x^{alpha}zeta(alpha))$ becomes $O(infty)$, which is vacuously true for any function of $x$.



In practice, the places you'll actually want to use this always come from values of $alpha$ for which the series for $zeta$ converges - namely, $alpha>1$. However, it's still true for $alpha<1$, using the definitionof $zeta$ by analytic continuation.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    OK, $alpha=1$ is special. $O(infty)$ is a rather meaningless proposition.
    $endgroup$
    – jmerry
    Jan 17 at 21:47
















0












$begingroup$

The thing is - as far as the implied limit there is concerned - for fixed $alpha$ as $x$ varies, $zeta(alpha)$ is just a number. $O(cf(x))=O(f(x))$ for any constant $c$ and function $f$.



As noted in the comments, $alpha=1$ is an exception; there, $O(x^{alpha}zeta(alpha))$ becomes $O(infty)$, which is vacuously true for any function of $x$.



In practice, the places you'll actually want to use this always come from values of $alpha$ for which the series for $zeta$ converges - namely, $alpha>1$. However, it's still true for $alpha<1$, using the definitionof $zeta$ by analytic continuation.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    OK, $alpha=1$ is special. $O(infty)$ is a rather meaningless proposition.
    $endgroup$
    – jmerry
    Jan 17 at 21:47














0












0








0





$begingroup$

The thing is - as far as the implied limit there is concerned - for fixed $alpha$ as $x$ varies, $zeta(alpha)$ is just a number. $O(cf(x))=O(f(x))$ for any constant $c$ and function $f$.



As noted in the comments, $alpha=1$ is an exception; there, $O(x^{alpha}zeta(alpha))$ becomes $O(infty)$, which is vacuously true for any function of $x$.



In practice, the places you'll actually want to use this always come from values of $alpha$ for which the series for $zeta$ converges - namely, $alpha>1$. However, it's still true for $alpha<1$, using the definitionof $zeta$ by analytic continuation.






share|cite|improve this answer











$endgroup$



The thing is - as far as the implied limit there is concerned - for fixed $alpha$ as $x$ varies, $zeta(alpha)$ is just a number. $O(cf(x))=O(f(x))$ for any constant $c$ and function $f$.



As noted in the comments, $alpha=1$ is an exception; there, $O(x^{alpha}zeta(alpha))$ becomes $O(infty)$, which is vacuously true for any function of $x$.



In practice, the places you'll actually want to use this always come from values of $alpha$ for which the series for $zeta$ converges - namely, $alpha>1$. However, it's still true for $alpha<1$, using the definitionof $zeta$ by analytic continuation.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Jan 17 at 21:50

























answered Jan 17 at 20:31









jmerryjmerry

10.6k1225




10.6k1225












  • $begingroup$
    OK, $alpha=1$ is special. $O(infty)$ is a rather meaningless proposition.
    $endgroup$
    – jmerry
    Jan 17 at 21:47


















  • $begingroup$
    OK, $alpha=1$ is special. $O(infty)$ is a rather meaningless proposition.
    $endgroup$
    – jmerry
    Jan 17 at 21:47
















$begingroup$
OK, $alpha=1$ is special. $O(infty)$ is a rather meaningless proposition.
$endgroup$
– jmerry
Jan 17 at 21:47




$begingroup$
OK, $alpha=1$ is special. $O(infty)$ is a rather meaningless proposition.
$endgroup$
– jmerry
Jan 17 at 21:47


















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