Minimum Normalizer












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Let $x_1ge x_2gedots ge x_n> 0$. What is the minimum value of $k$ such that $$frac{nkx_i}{x_1+dots+x_n}ge 1quad forall i.$$



I tried a bit hoping that $k=1+frac{1}{2}+dots+frac{1}{n}$ would work. But not getting any clue. Any hint is greatly appreciated.










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    0












    $begingroup$


    Let $x_1ge x_2gedots ge x_n> 0$. What is the minimum value of $k$ such that $$frac{nkx_i}{x_1+dots+x_n}ge 1quad forall i.$$



    I tried a bit hoping that $k=1+frac{1}{2}+dots+frac{1}{n}$ would work. But not getting any clue. Any hint is greatly appreciated.










    share|cite|improve this question









    $endgroup$















      0












      0








      0





      $begingroup$


      Let $x_1ge x_2gedots ge x_n> 0$. What is the minimum value of $k$ such that $$frac{nkx_i}{x_1+dots+x_n}ge 1quad forall i.$$



      I tried a bit hoping that $k=1+frac{1}{2}+dots+frac{1}{n}$ would work. But not getting any clue. Any hint is greatly appreciated.










      share|cite|improve this question









      $endgroup$




      Let $x_1ge x_2gedots ge x_n> 0$. What is the minimum value of $k$ such that $$frac{nkx_i}{x_1+dots+x_n}ge 1quad forall i.$$



      I tried a bit hoping that $k=1+frac{1}{2}+dots+frac{1}{n}$ would work. But not getting any clue. Any hint is greatly appreciated.







      calculus






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      asked Jan 13 at 12:06









      KumaraKumara

      221118




      221118






















          1 Answer
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          $begingroup$

          You want to find the minimum $k>0$ such that
          $$
          k, x_igeq overline{x}, quad forall i = 1, ldots, n,
          qquad
          text{where} overline{x} := frac{x_1 + cdots + x_n}{n},.
          $$

          Since, by assumption, $x_1 geq x_2 geq cdots geq x_n > 0$, the above $n$ inequalities are satisfied if and only if $k, x_n geq overline{x}$. Hence, the minimum of such values of $k$ is $k = overline{x} / x_n$.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            Sure, you are right, for some reason I was considering the reversed inequality!
            $endgroup$
            – Rigel
            Jan 13 at 12:49










          • $begingroup$
            Thanks. That's right. However, is it possible to obtain the bound in terms of $k=1+frac{1}{2}+dots+frac{1}{n}$ possibly with some multiplicative (constant) factor?
            $endgroup$
            – Kumara
            Jan 13 at 15:46













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          1 Answer
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          1 Answer
          1






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          active

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          1












          $begingroup$

          You want to find the minimum $k>0$ such that
          $$
          k, x_igeq overline{x}, quad forall i = 1, ldots, n,
          qquad
          text{where} overline{x} := frac{x_1 + cdots + x_n}{n},.
          $$

          Since, by assumption, $x_1 geq x_2 geq cdots geq x_n > 0$, the above $n$ inequalities are satisfied if and only if $k, x_n geq overline{x}$. Hence, the minimum of such values of $k$ is $k = overline{x} / x_n$.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            Sure, you are right, for some reason I was considering the reversed inequality!
            $endgroup$
            – Rigel
            Jan 13 at 12:49










          • $begingroup$
            Thanks. That's right. However, is it possible to obtain the bound in terms of $k=1+frac{1}{2}+dots+frac{1}{n}$ possibly with some multiplicative (constant) factor?
            $endgroup$
            – Kumara
            Jan 13 at 15:46


















          1












          $begingroup$

          You want to find the minimum $k>0$ such that
          $$
          k, x_igeq overline{x}, quad forall i = 1, ldots, n,
          qquad
          text{where} overline{x} := frac{x_1 + cdots + x_n}{n},.
          $$

          Since, by assumption, $x_1 geq x_2 geq cdots geq x_n > 0$, the above $n$ inequalities are satisfied if and only if $k, x_n geq overline{x}$. Hence, the minimum of such values of $k$ is $k = overline{x} / x_n$.






          share|cite|improve this answer











          $endgroup$













          • $begingroup$
            Sure, you are right, for some reason I was considering the reversed inequality!
            $endgroup$
            – Rigel
            Jan 13 at 12:49










          • $begingroup$
            Thanks. That's right. However, is it possible to obtain the bound in terms of $k=1+frac{1}{2}+dots+frac{1}{n}$ possibly with some multiplicative (constant) factor?
            $endgroup$
            – Kumara
            Jan 13 at 15:46
















          1












          1








          1





          $begingroup$

          You want to find the minimum $k>0$ such that
          $$
          k, x_igeq overline{x}, quad forall i = 1, ldots, n,
          qquad
          text{where} overline{x} := frac{x_1 + cdots + x_n}{n},.
          $$

          Since, by assumption, $x_1 geq x_2 geq cdots geq x_n > 0$, the above $n$ inequalities are satisfied if and only if $k, x_n geq overline{x}$. Hence, the minimum of such values of $k$ is $k = overline{x} / x_n$.






          share|cite|improve this answer











          $endgroup$



          You want to find the minimum $k>0$ such that
          $$
          k, x_igeq overline{x}, quad forall i = 1, ldots, n,
          qquad
          text{where} overline{x} := frac{x_1 + cdots + x_n}{n},.
          $$

          Since, by assumption, $x_1 geq x_2 geq cdots geq x_n > 0$, the above $n$ inequalities are satisfied if and only if $k, x_n geq overline{x}$. Hence, the minimum of such values of $k$ is $k = overline{x} / x_n$.







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited Jan 13 at 12:48

























          answered Jan 13 at 12:25









          RigelRigel

          11.2k11320




          11.2k11320












          • $begingroup$
            Sure, you are right, for some reason I was considering the reversed inequality!
            $endgroup$
            – Rigel
            Jan 13 at 12:49










          • $begingroup$
            Thanks. That's right. However, is it possible to obtain the bound in terms of $k=1+frac{1}{2}+dots+frac{1}{n}$ possibly with some multiplicative (constant) factor?
            $endgroup$
            – Kumara
            Jan 13 at 15:46




















          • $begingroup$
            Sure, you are right, for some reason I was considering the reversed inequality!
            $endgroup$
            – Rigel
            Jan 13 at 12:49










          • $begingroup$
            Thanks. That's right. However, is it possible to obtain the bound in terms of $k=1+frac{1}{2}+dots+frac{1}{n}$ possibly with some multiplicative (constant) factor?
            $endgroup$
            – Kumara
            Jan 13 at 15:46


















          $begingroup$
          Sure, you are right, for some reason I was considering the reversed inequality!
          $endgroup$
          – Rigel
          Jan 13 at 12:49




          $begingroup$
          Sure, you are right, for some reason I was considering the reversed inequality!
          $endgroup$
          – Rigel
          Jan 13 at 12:49












          $begingroup$
          Thanks. That's right. However, is it possible to obtain the bound in terms of $k=1+frac{1}{2}+dots+frac{1}{n}$ possibly with some multiplicative (constant) factor?
          $endgroup$
          – Kumara
          Jan 13 at 15:46






          $begingroup$
          Thanks. That's right. However, is it possible to obtain the bound in terms of $k=1+frac{1}{2}+dots+frac{1}{n}$ possibly with some multiplicative (constant) factor?
          $endgroup$
          – Kumara
          Jan 13 at 15:46




















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