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hbghlyj Posted at 2021-12-28 05:16:59 |Read mode
Last edited by hbghlyj at 2022-1-5 13:04:00$$\prod_{n=1}^{+\infty}\left(1+x^{2 n-1}\right)^{8}-\prod_{n=1}^{+\infty}\left(1-x^{2 n-1}\right)^{8}=16 x \prod_{n=1}^{+\infty}\left(1+x^{2 n}\right)^{8}$$ 这其实是theta函数的四次方和性质,相当于1/lambda(z)+1/lambda(z+1)=1</td></tr></table> </div> <div id="comment_42414" class="cm"> </div> <div id="post_rate_div_42414"></div> </div> </div> </td></tr> <tr><td class="plc plm"> </td> </tr> <tr id="_postposition42414"></tr> <tr> <td class="pls"></td> <td class="plc" style="overflow:visible;"> <div class="po hin"> <div class="pob cl"> <em> <a class="fastre" href="forum.php?mod=post&amp;action=reply&amp;fid=6&amp;tid=8440&amp;repquote=42414&amp;extra=page%3D1&amp;page=1" onclick="showWindow('reply', this.href)">Reply</a> <a class="editp" href="forum.php?mod=post&amp;action=edit&amp;fid=6&amp;tid=8440&amp;pid=42414&amp;page=1">Edit</a> </em> <p> <a href="javascript:;" onclick="showWindow('miscreport42414', 'misc.php?mod=report&rtype=post&rid=42414&tid=8440&fid=6', 'get', -1);return false;">Report</a> </p> </div> </div> </td> </tr> <tr class="ad"> <td class="pls"> </td> <td class="plc"> </td> </tr> </table> </div><div id="post_42535" ><table id="pid42535" class="plhin" summary="pid42535" cellspacing="0" cellpadding="0"> <tr> <td class="pls" rowspan="2"> <div id="favatar42535" class="pls cl favatar"> <div class="pi"> <div class="authi"><a href="space-uid-2861.html" target="_blank" class="xw1">hbghlyj</a> </div> </div> <div class="p_pop blk bui card_gender_2" id="userinfo42535" style="display: none; margin-top: -11px;"> <div class="m z"> <div id="userinfo42535_ma"></div> </div> <div class="i y"> <div> <strong><a href="space-uid-2861.html" target="_blank" class="xi2">hbghlyj</a></strong> <em>Offline</em> </div><dl class="cl"> <dt>Credits</dt><dd><a href="home.php?mod=space&uid=2861&do=profile" target="_blank" class="xi2">66163</a></dd> </dl><div class="imicn"> <a href="//wpa.qq.com/msgrd?v=3&amp;uin=15063662&amp;site=悠闲数学娱乐论坛(第3版)&amp;menu=yes&amp;from=discuz" target="_blank" title="QQ"><img src="static/image/common/qq.gif" alt="QQ" /></a><a href="javascript:;" onclick="window.open('//amos.im.alisoft.com/msg.aw?v=2&uid='+encodeURIComponent('阿里旺旺')+'&site=cntaobao&s=2&charset=utf-8')" title="Wangwang"><img src="static/image/common/taobao.gif" alt="Wangwang" /></a><a href="https://cjhb.site" target="_blank" title="'s Homepage"><img src="static/image/common/forumlink.gif" alt="'s Homepage" /></a><a href="home.php?mod=space&amp;uid=2861&amp;do=profile" target="_blank" title="View details"><img src="static/image/common/userinfo.gif" alt="View details" /></a> </div> <div id="avatarfeed"><span id="threadsortswait"></span></div> </div> </div> <div> <div class="avatar"><a href="space-uid-2861.html" class="avtm" target="_blank"><img src="./data/avatar/000/00/28/61_avatar_middle.jpg" class="user_avatar"></a></div> </div> <div class="tns xg2"><table cellspacing="0" cellpadding="0"><th><p><a href="home.php?mod=space&uid=2861&do=thread&type=thread&view=me&from=space" class="xi2">3147</a></p>Threads</th><th><p><a href="home.php?mod=space&uid=2861&do=thread&type=reply&view=me&from=space" class="xi2">8493</a></p>Posts</th><td><p><a href="home.php?mod=space&uid=2861&do=profile" class="xi2"><span title="66163">610K</span></a></p>Credits</td></table></div> <p><em><a href="home.php?mod=spacecp&amp;ac=usergroup&amp;gid=1" target="_blank"></a></em></p> <p><span></span></p> <dl class="pil cl"> <dt>Credits</dt><dd><a href="home.php?mod=space&uid=2861&do=profile" target="_blank" class="xi2">66163</a></dd> </dl> <dl class="pil cl"><a href="//wpa.qq.com/msgrd?v=3&uin=15063662&site=悠闲数学娱乐论坛(第3版)&menu=yes&from=discuz" target="_blank" title="Start QQ chat"><img src="static/image/common/qq_big.gif" alt="QQ" style="margin:0px;"/></a></dl><p style="font-size: 12px;"><a href="thread-8440-1-1.html" rel="nofollow">Show all posts</a></p> <ul class="xl xl2 o cl"> <li class="pm2"><a href="home.php?mod=spacecp&amp;ac=pm&amp;op=showmsg&amp;handlekey=showmsg_2861&amp;touid=2861&amp;pmid=0&amp;daterange=2&amp;pid=42535&amp;tid=8440" onclick="showWindow('sendpm', this.href);" title="Send PM" class="xi2">Send PM</a></li> </ul> </div> </td> <td class="plc"> <div class="pi"> <div class="pti"> <div class="pdbt"> </div> <div class="authi"> <em class="authicn fico-person fic4 fnmr vm" id="authicon42535" title="Author"></em> &nbsp;Author<span class="pipe">|</span> <a href="space-uid-2861.html" target="_blank" class="xi2 neiid">hbghlyj</a> <!-- kk edt --> <em id="authorposton42535">Posted at 2022-1-5 13:04:02</em> </div> </div> </div><div class="pct"><div class="pcb"> <div class="t_fsz"><table cellspacing="0" cellpadding="0"><tr><td class="t_f" id="postmessage_42535"> <i class="pstatus">Last edited by hbghlyj at 2022-1-5 13:14:00</i>
For $|x|<1$, prove $\prod_{n \geq 1}\left(\frac{1}{1+x^{n}} \frac{1}{1+x^{2 n-1}}\right)^{8}+16 \prod_{n \geq 1}\left(\frac{1+x^{2 n}}{1+x^{2 n-1}}\right)^{8}=1$
$-\sum_{n \geq 1} \frac{n q^{n}}{1-q^{n}}-8 \sum_{n \geq 1} \frac{n q^{4 n}}{1-q^{4 n}}+6 \sum_{n \geq 1} \frac{n q^{2 n}}{1-q^{2 n}}=\sum_{n \geq 1} \frac{2 n q^{2 n}}{1+q^{2 n}}-\sum_{n \geq 1} \frac{(2 n-1) q^{2 n-1}}{1+q^{2 n-1}}$

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kuing Posted at 2022-1-5 13:18:31
将两层连成一层

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kuing Posted at 2022-1-5 13:32:14
回复 4# hbghlyj

其实我也好奇那堆空的表格到底起了什么作用?

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青青子衿 Posted at 2022-1-7 10:35:45
Last edited by 青青子衿 at 2023-8-30 17:04:00\begin{align*}
\color{black}{\prod_{n=1}^{+\infty}\left[\left(1+q^{2 n-1}\right)^{8}\right]-\prod_{n=1}^{+\infty}\left[\left(1-q^{2 n-1}\right)^{8}\right]=16 q \prod_{n=1}^{+\infty}\left[\left(1+q^{2 n}\right)^{8}\right]}
\end{align*}
这个无穷乘积表达式好像和椭圆伊塔/西塔函数有关……

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Czhang271828 Posted at 2022-1-30 11:58:26
回复 6# 青青子衿

找到一位玩这个的老哥...

www-elsa.physik.uni-bonn.de/~dieckman/InfProd … vingxThetaxFunctions

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Czhang271828 Posted at 2022-8-9 21:06:43
An elementary proof without the knowlegde of $\eta$ -function, modular form, etc. Can be found in P155 in the book An Invitation to $q$ -Series. The book Eta Products and Theta Series Identities is one of my dictionaries in the study of modular form, where you can find the identity at page 152.
无钱佮歹看、无样佮歹生、无汉草佮无文采、无学历佮无能力、无高度无速度无力度共闲无代志。(闽南话)
口号:疼惜生命,远离内卷。

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青青子衿 Posted at 2023-5-15 15:46:40
Last edited by 青青子衿 at 2023-5-15 20:58:00
Czhang271828 发表于 2022-8-9 21:06
An elementary proof without the knowlegde of $\eta$ -function, modular form, etc. Can be found in  ...

\begin{align*}
\left.\partial_z\vartheta_1(z,q)\right|_{z=0}&=2 \sqrt[4]{q}\prod\limits_{i=1}^{+\infty\>\>}\left(1-q^{2 k}\right)^3\\
\vartheta_2(0,q)&=2 \sqrt[4]{q}\prod\limits_{i=1}^{+\infty\>\>}\left(1-q^{2 k}\right) \left(1+q^{2 k}\right)^2\\
\vartheta_3(0,q)&=\prod\limits_{i=1}^{+\infty\>\>}\left(1-q^{2 k}\right) \left(1+q^{2 k-1}\right)^2\\
\vartheta_4(0,q)&=\prod\limits_{i=1}^{+\infty\>\>}\left(1-q^{2 k}\right) \left(1-q^{2 k-1}\right)^2\\
\sqrt{k}&=\dfrac{\vartheta_2(0,q)}{\vartheta_3(0,q)}=2\sqrt[4]{q}\cdot\left[\dfrac{\prod\limits_{i=1}^{+\infty\>\>}(1+q^{2k})}{\prod\limits_{i=1}^{+\infty\>\>}(1+q^{2k-1})}\right]^2\\
\sqrt{k'}&=\dfrac{\vartheta_4(0,q)}{\vartheta_3(0,q)}=\left[\dfrac{\prod\limits_{i=1}^{+\infty\>\>}(1-q^{2k-1})}{\prod\limits_{i=1}^{+\infty\>\>}(1+q^{2k-1})}\right]^2\\
k^2+k'^2&=1
\end{align*}


  1. 2 q^(1/4) Product[(1 - q^(2 k))^3, {k, 1, +Infinity}] /. q -> 0.3
  2. EllipticThetaPrime[1, 0, 0.3]
  3. 2 q^(1/4) Product[(1 - q^(2 k)) (1 + q^(2 k))^2, {k,
  4.     1, +Infinity}] /. q -> 0.3
  5. EllipticTheta[2, 0, 0.3]
  6. Product[(1 - q^(2 k)) (1 + q^(2 k - 1))^2, {k, 1, +Infinity}] /.
  7. q -> 0.3
  8. EllipticTheta[3, 0, 0.3]
  9. Product[(1 - q^(2 k)) (1 - q^(2 k - 1))^2, {k, 1, +Infinity}] /.
  10. q -> 0.3
  11. EllipticTheta[4, 0, 0.3]
Copy the Code

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青青子衿 Posted at 2023-5-26 17:58:04
青青子衿 发表于 2022-1-7 10:35
\begin{align*}
\color{black}{\prod_{n=1}^{+\infty}\left[\left(1+q^{2 n-1}\right)^{8}\right]-\prod_{n=1}^{+\infty}\left[\left(1-q^{2 n-1}\right)^{8}\right]=16 q \prod_{n=1}^{+\infty}\left[\left(1+q^{2 n}\right)^{8}\right]}
\end{align*}
...
An Identity Relating a Theta Function to a Sum of Lambert Series
researchgate.net/publication/228887537_An_Ide … um_of_Lambert_Series

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