Sums of two squares in arithmetic progressions












9












$begingroup$


Let $r(n)$ denote the number of representations of $n$ as the sum of two squares. Are there any known results on $$sum _{nleq xatop {nequiv a(q)}}r(n)$$ and in particular is there an asymptotic formula?










share|cite|improve this question











$endgroup$












  • $begingroup$
    If we fix $a, q$ and increase $x$, isn't this essentially the Gauss circle problem with some shift in the lattice?
    $endgroup$
    – Dongryul Kim
    Apr 2 at 12:50










  • $begingroup$
    It would be nice to make clear whether you require uniformity in $a$ and $q$. If yes, then the answer of Ofir addresses this. If not, then the result is a simple application of Dirichlet series techniques.
    $endgroup$
    – Daniel Loughran
    Apr 2 at 19:10
















9












$begingroup$


Let $r(n)$ denote the number of representations of $n$ as the sum of two squares. Are there any known results on $$sum _{nleq xatop {nequiv a(q)}}r(n)$$ and in particular is there an asymptotic formula?










share|cite|improve this question











$endgroup$












  • $begingroup$
    If we fix $a, q$ and increase $x$, isn't this essentially the Gauss circle problem with some shift in the lattice?
    $endgroup$
    – Dongryul Kim
    Apr 2 at 12:50










  • $begingroup$
    It would be nice to make clear whether you require uniformity in $a$ and $q$. If yes, then the answer of Ofir addresses this. If not, then the result is a simple application of Dirichlet series techniques.
    $endgroup$
    – Daniel Loughran
    Apr 2 at 19:10














9












9








9


1



$begingroup$


Let $r(n)$ denote the number of representations of $n$ as the sum of two squares. Are there any known results on $$sum _{nleq xatop {nequiv a(q)}}r(n)$$ and in particular is there an asymptotic formula?










share|cite|improve this question











$endgroup$




Let $r(n)$ denote the number of representations of $n$ as the sum of two squares. Are there any known results on $$sum _{nleq xatop {nequiv a(q)}}r(n)$$ and in particular is there an asymptotic formula?







nt.number-theory reference-request analytic-number-theory arithmetic-progression sums-of-squares






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Apr 2 at 19:33









GH from MO

59.3k5148227




59.3k5148227










asked Apr 2 at 12:30









cawscaws

734




734












  • $begingroup$
    If we fix $a, q$ and increase $x$, isn't this essentially the Gauss circle problem with some shift in the lattice?
    $endgroup$
    – Dongryul Kim
    Apr 2 at 12:50










  • $begingroup$
    It would be nice to make clear whether you require uniformity in $a$ and $q$. If yes, then the answer of Ofir addresses this. If not, then the result is a simple application of Dirichlet series techniques.
    $endgroup$
    – Daniel Loughran
    Apr 2 at 19:10


















  • $begingroup$
    If we fix $a, q$ and increase $x$, isn't this essentially the Gauss circle problem with some shift in the lattice?
    $endgroup$
    – Dongryul Kim
    Apr 2 at 12:50










  • $begingroup$
    It would be nice to make clear whether you require uniformity in $a$ and $q$. If yes, then the answer of Ofir addresses this. If not, then the result is a simple application of Dirichlet series techniques.
    $endgroup$
    – Daniel Loughran
    Apr 2 at 19:10
















$begingroup$
If we fix $a, q$ and increase $x$, isn't this essentially the Gauss circle problem with some shift in the lattice?
$endgroup$
– Dongryul Kim
Apr 2 at 12:50




$begingroup$
If we fix $a, q$ and increase $x$, isn't this essentially the Gauss circle problem with some shift in the lattice?
$endgroup$
– Dongryul Kim
Apr 2 at 12:50












$begingroup$
It would be nice to make clear whether you require uniformity in $a$ and $q$. If yes, then the answer of Ofir addresses this. If not, then the result is a simple application of Dirichlet series techniques.
$endgroup$
– Daniel Loughran
Apr 2 at 19:10




$begingroup$
It would be nice to make clear whether you require uniformity in $a$ and $q$. If yes, then the answer of Ofir addresses this. If not, then the result is a simple application of Dirichlet series techniques.
$endgroup$
– Daniel Loughran
Apr 2 at 19:10










1 Answer
1






active

oldest

votes


















16












$begingroup$

The first result in this direction seems to be due to R. A. Smith, ``The Circle Problem in an Arithmetic Progression,'' Can. Math. Bull. 11 (2), 175–184 (1968). He showed that if we write
$$sum _{nleq xatop {nequiv a(q)}}r(n) =pi x cdot frac{eta_{a}(q)}{q^2}+ R_{q,a}(x)$$
where $eta_{a}(q) := { (x_1,x_2) in (mathbb{Z}/qmathbb{Z)}^2 : x_1^2 +x_2^2 equiv a bmod q}$, then
$$R_{q,a}(x) = Oleft( x^{frac{2}{3} + xi} q^{-frac{1}{2}(1+3xi)}gcd(a,q)^{1/2}tau(q) right)$$
for any $xi in (0,1/3)$. This is non-trivial for $q le x^{frac{2}{3}-varepsilon}$. In particular, as $x$ tends to infinity, your expression is asymptotic to $pi x$ times the probability that $x_1^2+x_2^2 equiv a bmod q$ (for uniformly drawn $x_1,x_2$ mod $q$). If you consider $a$ and $q$ as fixed, this answers your question.



The state-of-the-art result is due to D. I. Tolev, ``On the remainder term in the circle problem in an arithmetic progression,'' Tr. Mat. Inst. Steklova 276 (2012), Teoriya Chisel, Algebra i Analiz, 266--279; translation in Proc. Steklov Inst. Math. 276 (2012), no. 1, 261–274. He showed that
$$R_{q,a}(x) = Oleft( (q^{frac{1}{2}}+x^{frac{1}{3}}) gcd(a,q)^{1/2}tau^4(q)log^4 x right).$$
Interestingly, for $a=1$, there is a result which is superior in certain ranges of $x$ and $q$, see P. D. Varbanets, “Lattice Points in a Circle Whose Distances from the Center Are in an Arithmetic Progression,” Mat. Zametki 8 (6), 787–798 (1970) [Math. Notes 8, 917–923 (1970)].



All three results are explained in Tolev's paper.





In the 2002 PhD thesis of Michael J. Dancs under R. Vaughn, titled "On a Variance arising in the Gauss Circle Problem", he proves (independently of the above) that
$$f(q,a):=lim_{x to infty} frac{sum _{nleq xatop {nequiv a(q)}}r(n) }{pi x}$$
exists and can be written as
$$f(q,a)=q^{-3} sum_{k=1}^{q} expleft( 2pi i frac{-ak}{q} right) S(q,k)^2,$$
where $S(q,a)$ is a quadratic Gauss sum mod $q$. This gives a different expression for $eta_a(q)/q^2$, which was better suited for the applications given by Dancs. This is done in Theorem 2.1. He then proceeds to prove, in Theorem 2.2, the estimate
$$R_{q,a}(x) = Oleft( (sqrt{x}+q) log qright).$$
For small $q$ this is better than Smith's work. Still, it is superseded by Tolev's estimates.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    Thanks for the very informative answer!
    $endgroup$
    – caws
    Apr 2 at 21:42












Your Answer





StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "504"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});














draft saved

draft discarded


















StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmathoverflow.net%2fquestions%2f326964%2fsums-of-two-squares-in-arithmetic-progressions%23new-answer', 'question_page');
}
);

Post as a guest















Required, but never shown

























1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









16












$begingroup$

The first result in this direction seems to be due to R. A. Smith, ``The Circle Problem in an Arithmetic Progression,'' Can. Math. Bull. 11 (2), 175–184 (1968). He showed that if we write
$$sum _{nleq xatop {nequiv a(q)}}r(n) =pi x cdot frac{eta_{a}(q)}{q^2}+ R_{q,a}(x)$$
where $eta_{a}(q) := { (x_1,x_2) in (mathbb{Z}/qmathbb{Z)}^2 : x_1^2 +x_2^2 equiv a bmod q}$, then
$$R_{q,a}(x) = Oleft( x^{frac{2}{3} + xi} q^{-frac{1}{2}(1+3xi)}gcd(a,q)^{1/2}tau(q) right)$$
for any $xi in (0,1/3)$. This is non-trivial for $q le x^{frac{2}{3}-varepsilon}$. In particular, as $x$ tends to infinity, your expression is asymptotic to $pi x$ times the probability that $x_1^2+x_2^2 equiv a bmod q$ (for uniformly drawn $x_1,x_2$ mod $q$). If you consider $a$ and $q$ as fixed, this answers your question.



The state-of-the-art result is due to D. I. Tolev, ``On the remainder term in the circle problem in an arithmetic progression,'' Tr. Mat. Inst. Steklova 276 (2012), Teoriya Chisel, Algebra i Analiz, 266--279; translation in Proc. Steklov Inst. Math. 276 (2012), no. 1, 261–274. He showed that
$$R_{q,a}(x) = Oleft( (q^{frac{1}{2}}+x^{frac{1}{3}}) gcd(a,q)^{1/2}tau^4(q)log^4 x right).$$
Interestingly, for $a=1$, there is a result which is superior in certain ranges of $x$ and $q$, see P. D. Varbanets, “Lattice Points in a Circle Whose Distances from the Center Are in an Arithmetic Progression,” Mat. Zametki 8 (6), 787–798 (1970) [Math. Notes 8, 917–923 (1970)].



All three results are explained in Tolev's paper.





In the 2002 PhD thesis of Michael J. Dancs under R. Vaughn, titled "On a Variance arising in the Gauss Circle Problem", he proves (independently of the above) that
$$f(q,a):=lim_{x to infty} frac{sum _{nleq xatop {nequiv a(q)}}r(n) }{pi x}$$
exists and can be written as
$$f(q,a)=q^{-3} sum_{k=1}^{q} expleft( 2pi i frac{-ak}{q} right) S(q,k)^2,$$
where $S(q,a)$ is a quadratic Gauss sum mod $q$. This gives a different expression for $eta_a(q)/q^2$, which was better suited for the applications given by Dancs. This is done in Theorem 2.1. He then proceeds to prove, in Theorem 2.2, the estimate
$$R_{q,a}(x) = Oleft( (sqrt{x}+q) log qright).$$
For small $q$ this is better than Smith's work. Still, it is superseded by Tolev's estimates.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    Thanks for the very informative answer!
    $endgroup$
    – caws
    Apr 2 at 21:42
















16












$begingroup$

The first result in this direction seems to be due to R. A. Smith, ``The Circle Problem in an Arithmetic Progression,'' Can. Math. Bull. 11 (2), 175–184 (1968). He showed that if we write
$$sum _{nleq xatop {nequiv a(q)}}r(n) =pi x cdot frac{eta_{a}(q)}{q^2}+ R_{q,a}(x)$$
where $eta_{a}(q) := { (x_1,x_2) in (mathbb{Z}/qmathbb{Z)}^2 : x_1^2 +x_2^2 equiv a bmod q}$, then
$$R_{q,a}(x) = Oleft( x^{frac{2}{3} + xi} q^{-frac{1}{2}(1+3xi)}gcd(a,q)^{1/2}tau(q) right)$$
for any $xi in (0,1/3)$. This is non-trivial for $q le x^{frac{2}{3}-varepsilon}$. In particular, as $x$ tends to infinity, your expression is asymptotic to $pi x$ times the probability that $x_1^2+x_2^2 equiv a bmod q$ (for uniformly drawn $x_1,x_2$ mod $q$). If you consider $a$ and $q$ as fixed, this answers your question.



The state-of-the-art result is due to D. I. Tolev, ``On the remainder term in the circle problem in an arithmetic progression,'' Tr. Mat. Inst. Steklova 276 (2012), Teoriya Chisel, Algebra i Analiz, 266--279; translation in Proc. Steklov Inst. Math. 276 (2012), no. 1, 261–274. He showed that
$$R_{q,a}(x) = Oleft( (q^{frac{1}{2}}+x^{frac{1}{3}}) gcd(a,q)^{1/2}tau^4(q)log^4 x right).$$
Interestingly, for $a=1$, there is a result which is superior in certain ranges of $x$ and $q$, see P. D. Varbanets, “Lattice Points in a Circle Whose Distances from the Center Are in an Arithmetic Progression,” Mat. Zametki 8 (6), 787–798 (1970) [Math. Notes 8, 917–923 (1970)].



All three results are explained in Tolev's paper.





In the 2002 PhD thesis of Michael J. Dancs under R. Vaughn, titled "On a Variance arising in the Gauss Circle Problem", he proves (independently of the above) that
$$f(q,a):=lim_{x to infty} frac{sum _{nleq xatop {nequiv a(q)}}r(n) }{pi x}$$
exists and can be written as
$$f(q,a)=q^{-3} sum_{k=1}^{q} expleft( 2pi i frac{-ak}{q} right) S(q,k)^2,$$
where $S(q,a)$ is a quadratic Gauss sum mod $q$. This gives a different expression for $eta_a(q)/q^2$, which was better suited for the applications given by Dancs. This is done in Theorem 2.1. He then proceeds to prove, in Theorem 2.2, the estimate
$$R_{q,a}(x) = Oleft( (sqrt{x}+q) log qright).$$
For small $q$ this is better than Smith's work. Still, it is superseded by Tolev's estimates.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    Thanks for the very informative answer!
    $endgroup$
    – caws
    Apr 2 at 21:42














16












16








16





$begingroup$

The first result in this direction seems to be due to R. A. Smith, ``The Circle Problem in an Arithmetic Progression,'' Can. Math. Bull. 11 (2), 175–184 (1968). He showed that if we write
$$sum _{nleq xatop {nequiv a(q)}}r(n) =pi x cdot frac{eta_{a}(q)}{q^2}+ R_{q,a}(x)$$
where $eta_{a}(q) := { (x_1,x_2) in (mathbb{Z}/qmathbb{Z)}^2 : x_1^2 +x_2^2 equiv a bmod q}$, then
$$R_{q,a}(x) = Oleft( x^{frac{2}{3} + xi} q^{-frac{1}{2}(1+3xi)}gcd(a,q)^{1/2}tau(q) right)$$
for any $xi in (0,1/3)$. This is non-trivial for $q le x^{frac{2}{3}-varepsilon}$. In particular, as $x$ tends to infinity, your expression is asymptotic to $pi x$ times the probability that $x_1^2+x_2^2 equiv a bmod q$ (for uniformly drawn $x_1,x_2$ mod $q$). If you consider $a$ and $q$ as fixed, this answers your question.



The state-of-the-art result is due to D. I. Tolev, ``On the remainder term in the circle problem in an arithmetic progression,'' Tr. Mat. Inst. Steklova 276 (2012), Teoriya Chisel, Algebra i Analiz, 266--279; translation in Proc. Steklov Inst. Math. 276 (2012), no. 1, 261–274. He showed that
$$R_{q,a}(x) = Oleft( (q^{frac{1}{2}}+x^{frac{1}{3}}) gcd(a,q)^{1/2}tau^4(q)log^4 x right).$$
Interestingly, for $a=1$, there is a result which is superior in certain ranges of $x$ and $q$, see P. D. Varbanets, “Lattice Points in a Circle Whose Distances from the Center Are in an Arithmetic Progression,” Mat. Zametki 8 (6), 787–798 (1970) [Math. Notes 8, 917–923 (1970)].



All three results are explained in Tolev's paper.





In the 2002 PhD thesis of Michael J. Dancs under R. Vaughn, titled "On a Variance arising in the Gauss Circle Problem", he proves (independently of the above) that
$$f(q,a):=lim_{x to infty} frac{sum _{nleq xatop {nequiv a(q)}}r(n) }{pi x}$$
exists and can be written as
$$f(q,a)=q^{-3} sum_{k=1}^{q} expleft( 2pi i frac{-ak}{q} right) S(q,k)^2,$$
where $S(q,a)$ is a quadratic Gauss sum mod $q$. This gives a different expression for $eta_a(q)/q^2$, which was better suited for the applications given by Dancs. This is done in Theorem 2.1. He then proceeds to prove, in Theorem 2.2, the estimate
$$R_{q,a}(x) = Oleft( (sqrt{x}+q) log qright).$$
For small $q$ this is better than Smith's work. Still, it is superseded by Tolev's estimates.






share|cite|improve this answer











$endgroup$



The first result in this direction seems to be due to R. A. Smith, ``The Circle Problem in an Arithmetic Progression,'' Can. Math. Bull. 11 (2), 175–184 (1968). He showed that if we write
$$sum _{nleq xatop {nequiv a(q)}}r(n) =pi x cdot frac{eta_{a}(q)}{q^2}+ R_{q,a}(x)$$
where $eta_{a}(q) := { (x_1,x_2) in (mathbb{Z}/qmathbb{Z)}^2 : x_1^2 +x_2^2 equiv a bmod q}$, then
$$R_{q,a}(x) = Oleft( x^{frac{2}{3} + xi} q^{-frac{1}{2}(1+3xi)}gcd(a,q)^{1/2}tau(q) right)$$
for any $xi in (0,1/3)$. This is non-trivial for $q le x^{frac{2}{3}-varepsilon}$. In particular, as $x$ tends to infinity, your expression is asymptotic to $pi x$ times the probability that $x_1^2+x_2^2 equiv a bmod q$ (for uniformly drawn $x_1,x_2$ mod $q$). If you consider $a$ and $q$ as fixed, this answers your question.



The state-of-the-art result is due to D. I. Tolev, ``On the remainder term in the circle problem in an arithmetic progression,'' Tr. Mat. Inst. Steklova 276 (2012), Teoriya Chisel, Algebra i Analiz, 266--279; translation in Proc. Steklov Inst. Math. 276 (2012), no. 1, 261–274. He showed that
$$R_{q,a}(x) = Oleft( (q^{frac{1}{2}}+x^{frac{1}{3}}) gcd(a,q)^{1/2}tau^4(q)log^4 x right).$$
Interestingly, for $a=1$, there is a result which is superior in certain ranges of $x$ and $q$, see P. D. Varbanets, “Lattice Points in a Circle Whose Distances from the Center Are in an Arithmetic Progression,” Mat. Zametki 8 (6), 787–798 (1970) [Math. Notes 8, 917–923 (1970)].



All three results are explained in Tolev's paper.





In the 2002 PhD thesis of Michael J. Dancs under R. Vaughn, titled "On a Variance arising in the Gauss Circle Problem", he proves (independently of the above) that
$$f(q,a):=lim_{x to infty} frac{sum _{nleq xatop {nequiv a(q)}}r(n) }{pi x}$$
exists and can be written as
$$f(q,a)=q^{-3} sum_{k=1}^{q} expleft( 2pi i frac{-ak}{q} right) S(q,k)^2,$$
where $S(q,a)$ is a quadratic Gauss sum mod $q$. This gives a different expression for $eta_a(q)/q^2$, which was better suited for the applications given by Dancs. This is done in Theorem 2.1. He then proceeds to prove, in Theorem 2.2, the estimate
$$R_{q,a}(x) = Oleft( (sqrt{x}+q) log qright).$$
For small $q$ this is better than Smith's work. Still, it is superseded by Tolev's estimates.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Apr 2 at 14:08

























answered Apr 2 at 13:27









Ofir GorodetskyOfir Gorodetsky

5,90312639




5,90312639












  • $begingroup$
    Thanks for the very informative answer!
    $endgroup$
    – caws
    Apr 2 at 21:42


















  • $begingroup$
    Thanks for the very informative answer!
    $endgroup$
    – caws
    Apr 2 at 21:42
















$begingroup$
Thanks for the very informative answer!
$endgroup$
– caws
Apr 2 at 21:42




$begingroup$
Thanks for the very informative answer!
$endgroup$
– caws
Apr 2 at 21:42


















draft saved

draft discarded




















































Thanks for contributing an answer to MathOverflow!


  • Please be sure to answer the question. Provide details and share your research!

But avoid



  • Asking for help, clarification, or responding to other answers.

  • Making statements based on opinion; back them up with references or personal experience.


Use MathJax to format equations. MathJax reference.


To learn more, see our tips on writing great answers.




draft saved


draft discarded














StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmathoverflow.net%2fquestions%2f326964%2fsums-of-two-squares-in-arithmetic-progressions%23new-answer', 'question_page');
}
);

Post as a guest















Required, but never shown





















































Required, but never shown














Required, but never shown












Required, but never shown







Required, but never shown

































Required, but never shown














Required, but never shown












Required, but never shown







Required, but never shown







Popular posts from this blog

Biblatex bibliography style without URLs when DOI exists (in Overleaf with Zotero bibliography)

ComboBox Display Member on multiple fields

Is it possible to collect Nectar points via Trainline?