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 <title>Open Problem Garden - Inequality of complex numbers - Comments</title>
 <link>http://openproblemgarden.org/op/inequality_of_complex_numbers</link>
 <description>Comments for &quot;Inequality of complex numbers&quot;</description>
 <language>en</language>
<item>
 <title>Yes, such  exists, say   (re: Inequality of complex numbers)</title>
 <link>http://openproblemgarden.org/op/inequality_of_complex_numbers#comment-6886</link>
 <description>&lt;p&gt;Yes, such &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/dccee841f3f498c2c58fa6ae1c1403c5a88c5b8d.png&quot; alt=&quot;$ c $&quot; /&gt; exists, say &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/7b2b3002d85bef106be8b075107d6e7a5f58a168.png&quot; alt=&quot;$ c=1000000 $&quot; /&gt; works. Assume the contrary and consider the counterexample. Without loss of generality, &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/d3c082893fea47de006e2705579e3a430559fcdf.png&quot; alt=&quot;$ \max |z_i|=1 $&quot; /&gt;, else multiple all &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/7db01f9707e4eb937bcb3cdf30844052ce534ebe.png&quot; alt=&quot;$ z_i $&quot; /&gt;&#039;s to some &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/1c5495e8d5fad095cf26610f2743d2a18cc36d40.png&quot; alt=&quot;$ \lambda&amp;gt;1 $&quot; /&gt; so that this bacomes true, LHS is multiplied by &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/4df9c754d756fe1a17b623cea7af01af487b6626.png&quot; alt=&quot;$ \lambda^n $&quot; /&gt;, while RHS only by &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/4f0c6c67f8c2c5d790253ebaa0753fa37f9df880.png&quot; alt=&quot;$ \lambda^2 $&quot; /&gt;. So, we again get a counterexample. Denote &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/bbe8450f330ec055b7e47c4275c003a75c66b7f1.png&quot; alt=&quot;$ \bar{z}=a $&quot; /&gt;, &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/4852323c4d64b39108199e4ca81c9740cb179e46.png&quot; alt=&quot;$ z_i=a+y_i $&quot; /&gt;, &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/5e259a3d76d3e332e6298d4c68f54056b5dc8759.png&quot; alt=&quot;$ \sum y_i=0 $&quot; /&gt;. Since LHS does not exceed 2, we have &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/43418d54a03a356ed6d18879dc15ab8899183f82.png&quot; alt=&quot;$ |y_i|&amp;lt;1/100 $&quot; /&gt; (else RHS is too large). Hence &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/2bf3fa3db2ed092909a9fc2c60a8e181f4da5904.png&quot; alt=&quot;$ |a|=|z_i-y_i|&amp;gt;1-1/100 $&quot; /&gt; for &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/ca49c241ece07915c97a31774a977841c6f0414c.png&quot; alt=&quot;$ i $&quot; /&gt; s.t. &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/0741cdd8fa8b6a68d837f5b204d3be8f7097d437.png&quot; alt=&quot;$ |z_i|=1 $&quot; /&gt;. Then we have &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/463cef67071865c7598e5fb2d918755349fef049.png&quot; alt=&quot;$ a+y_i=a(1+y_i/a)=ae^{y_i/a+p_i} $&quot; /&gt;, where &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/b3d40839194d06a01bf57f84a8a7042e9329dc1b.png&quot; alt=&quot;$ p_i=\ln(1+y_i/a)-y_i/a=(y_i/a)^2/2+(y_i/a)^3/3+\dots $&quot; /&gt;, &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/28413b12d287221634009073a2d4a421c5006b04.png&quot; alt=&quot;$ |p_i|\leq 2|y_i^2| $&quot; /&gt; by some easy estimate. Finally, LHS equals &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/237efd0a0dab8745d2410e5c17f9340f96e90950.png&quot; alt=&quot;$$ |a^n|(e^{p_1+p_2+\dots+p_n}-1), $$&quot; /&gt; and we just use estimate &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/eb0b57554e48eb74a6d4091d7724694531f89cbf.png&quot; alt=&quot;$ |e^p-1|\leq 2p $&quot; /&gt; for small enough &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/3a61100e933ba8a385afb74bfec47649b3daf522.png&quot; alt=&quot;$ p=p_1+p_2+\dots+p_n $&quot; /&gt; (&lt;img class=&quot;teximage&quot; src=&quot;/files/tex/928cd9d544fdea62f88a627aaee28c416c4366c0.png&quot; alt=&quot;$ p $&quot; /&gt; is small enough, since &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/ad300c67d9758cd82c5a428f6e56ed653f79f203.png&quot; alt=&quot;$ |p|\leq 2\sum |y_i^2|=\frac2{c}RHS\leq \frac4{c} $&quot; /&gt;).&lt;/p&gt;
</description>
 <pubDate>Wed, 05 Jan 2011 13:01:40 +0100</pubDate>
 <dc:creator>fedorpetrov</dc:creator>
 <guid isPermaLink="false">comment 6886 at http://openproblemgarden.org</guid>
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<item>
 <title>A hint  (re: Inequality of complex numbers)</title>
 <link>http://openproblemgarden.org/op/inequality_of_complex_numbers#comment-6769</link>
 <description>&lt;p&gt;I am the author of this hint and somehow mismanaged the posting. So here it is again:&lt;/p&gt;
&lt;p&gt;Let &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/8f47d7c6c6ceafab060ee0546da1f59de2865faf.png&quot; alt=&quot;$ z_k=\bar z + \epsilon a_k $&quot; /&gt; with &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/816b3cebf962fcc001285ab8e9adce8656388718.png&quot; alt=&quot;$ \epsilon $&quot; /&gt; small and &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/822a80fcf4fa4504feeb713d1891a79ebd1d3394.png&quot; alt=&quot;$ \sum_k a_k=0 $&quot; /&gt;. Then &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/e69218ba99a55ff6875b8b0739eb0ac80aa7b58d.png&quot; alt=&quot;$$\prod_k z_k - \bar z^n = \epsilon^2 \bar z^{n-2}\sum_{j&amp;lt;k}a_j a_k + ?\epsilon^3$$&quot; /&gt; and &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/bbce17272ecdea1a4d548d325f890f719151b9eb.png&quot; alt=&quot;$ |z_k-\bar z|^2=\epsilon^2|a_k|^2 $&quot; /&gt;.&lt;/p&gt;
&lt;p&gt;Now from &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/822a80fcf4fa4504feeb713d1891a79ebd1d3394.png&quot; alt=&quot;$ \sum_k a_k=0 $&quot; /&gt; it follows that &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/cb3248c51a987c979bd77b461f3867360e0bbbbd.png&quot; alt=&quot;$$|\sum_{j&amp;lt;k} a_j a_k| \le {1\over2} \sum_k|a_k|^2.$$&quot; /&gt; This shows that your inequality has the &quot;right order of magnitude&quot; with &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/6d18d53511640b942d1a2da5899030213e2d5570.png&quot; alt=&quot;$ c={1\over2} $&quot; /&gt;.&lt;/p&gt;
</description>
 <pubDate>Sun, 01 Aug 2010 14:15:48 +0200</pubDate>
 <dc:creator>Christian Blatter</dc:creator>
 <guid isPermaLink="false">comment 6769 at http://openproblemgarden.org</guid>
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<item>
 <title>A hint: \par Let  with   (re: Inequality of complex numbers)</title>
 <link>http://openproblemgarden.org/op/inequality_of_complex_numbers#comment-6767</link>
 <description>&lt;p&gt;A hint: \par Let &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/150e1e313a901ea5009899b6ef1cbab842e9a119.png&quot; alt=&quot;$ z_k=\bar z+\epsilon a_k $&quot; /&gt; with &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/816b3cebf962fcc001285ab8e9adce8656388718.png&quot; alt=&quot;$ \epsilon $&quot; /&gt; small and &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/822a80fcf4fa4504feeb713d1891a79ebd1d3394.png&quot; alt=&quot;$ \sum_k a_k=0 $&quot; /&gt;. Then  &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/3ca10733e3d7b7addf8209660f2a61607511655e.png&quot; alt=&quot;$$\product_k z_k - \bar z^n = \epsilon^2 \bar z^{n-2} \sum_{j&amp;lt;k} a_j a_k + ?\epsilon^3$$&quot; /&gt; and &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/0ebc197df33edb278c90e60b626c71acb51fc313.png&quot; alt=&quot;$ |z_k - \bar z|^2 = \epsilon^2 |a_k|^2 $&quot; /&gt;. \par Now from &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/822a80fcf4fa4504feeb713d1891a79ebd1d3394.png&quot; alt=&quot;$ \sum_k a_k=0 $&quot; /&gt; it follows that &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/e035c9e0fefc446f6a08da1126636504f5d667f9.png&quot; alt=&quot;$$| \sum_{j&amp;lt;k} a_j a_k | \le {1\over 2} \sum_k |a_k|^2 .$$&quot; /&gt; This shows that your inequality has ``the right order of magnitude&#039;&#039; with &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/147501c379085393b020e92035edfa95607a6742.png&quot; alt=&quot;$ c={1\over 2} $&quot; /&gt;.&lt;/p&gt;
</description>
 <pubDate>Thu, 29 Jul 2010 12:22:45 +0200</pubDate>
 <dc:creator>Anonymous</dc:creator>
 <guid isPermaLink="false">comment 6767 at http://openproblemgarden.org</guid>
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<item>
 <title>Requesting background information  (re: Inequality of complex numbers)</title>
 <link>http://openproblemgarden.org/op/inequality_of_complex_numbers#comment-6722</link>
 <description>&lt;p&gt;To feanor, the author of this conjecture:&lt;/p&gt;
&lt;p&gt;What is the motivation for this conjecture ?  The selected importance &quot;medium&quot; let me assume the verification or falsification of this conjecture would bring some benefit. If possible, describe that benefit (&quot;practical&quot; applications or consequences), please.  &lt;/p&gt;
</description>
 <pubDate>Wed, 21 Apr 2010 03:38:28 +0200</pubDate>
 <dc:creator>Carolus</dc:creator>
 <guid isPermaLink="false">comment 6722 at http://openproblemgarden.org</guid>
</item>
<item>
 <title>Inequality of complex numbers</title>
 <link>http://openproblemgarden.org/op/inequality_of_complex_numbers</link>
 <description>&lt;table cellspacing=&quot;10&quot;&gt;
&lt;tr&gt;
  &lt;td&gt;
    Author(s):
        &lt;a href=&quot;/kpz_equation_central_limit_theorem&quot;&gt;&lt;/a&gt;&amp;nbsp;&amp;nbsp;
  &lt;/td&gt;
  &lt;td align=right&gt;
    Subject:
        &lt;a href=&quot;/category/analysis&quot;&gt;Analysis&lt;/a&gt;&amp;nbsp;&amp;nbsp;
  &lt;/td&gt;
&lt;/tr&gt;

&lt;tr&gt;
  &lt;td colspan=2&gt;
    &lt;table border=1 cellspacing=&quot;5&quot;&gt;
      &lt;tr&gt;&lt;td&gt;
        &lt;div class=&quot;envtheorem&quot;&gt;&lt;b&gt;Conjecture&lt;/b&gt;&amp;nbsp;&amp;nbsp; There exists a real positive &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/dccee841f3f498c2c58fa6ae1c1403c5a88c5b8d.png&quot; alt=&quot;$ c $&quot; /&gt;, such that for any &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/6ab85c2397977f785c3874c9665c18848ddef70d.png&quot; alt=&quot;$ n\in\mathbb{N} $&quot; /&gt; and any &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/74292adfd82ef7e1d3d634a852bd9b90bc17b743.png&quot; alt=&quot;$ z_i\in\mathbb{C} $&quot; /&gt; where &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/d830a710a3211821ddf6f9632cf0af362a02942c.png&quot; alt=&quot;$ |z_i|\le 1 $&quot; /&gt; for &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/3282f6c94ba622752c04e64c4bd697299e8219ff.png&quot; alt=&quot;$ 1\le i\le n $&quot; /&gt; and  &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/c58de6dddeab0f501f20f8cb044babef37a4007f.png&quot; alt=&quot;$ \~z:=\frac{1}{n}\sum^n_{k=1}z_k $&quot; /&gt;, the following holds: &lt;img class=&quot;teximage&quot; src=&quot;/files/tex/524ebfaf6165fdbca63d19be83aa1db754af050e.png&quot; alt=&quot;$$\left|\prod^n_{k=1}z_k - \~z^n\right| \le c\cdot\sum^n_{k=1}|z_k-\~z|^2$$&quot; /&gt; &lt;/div&gt;

      &lt;/tr&gt;&lt;/td&gt;
    &lt;/table&gt;
  &lt;/td&gt;
&lt;/tr&gt;
&lt;/table&gt;</description>
 <category domain="http://openproblemgarden.org/category/analysis">Analysis</category>
 <comments>http://openproblemgarden.org/op/inequality_of_complex_numbers#comment</comments>
 <pubDate>Wed, 07 Apr 2010 13:06:06 +0200</pubDate>
 <dc:creator>feanor</dc:creator>
 <guid isPermaLink="false">37202 at http://openproblemgarden.org</guid>
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