Limes superior of $X_n>alpha ln(n)$












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Given the random variable $X_n$, to be exponential distributed with parameter $1$, we define
$$A_n:=left{X_n>alpha ln(n)right}.$$
We've shown in the classes that for $alpha leq 1$, $A_n$ occurs infinitely times, and for $alpha>1$ finitely times. Now calculating the limes superior $overline{lim}_{nrightarrowinfty}frac{X_n}{ln(n)}$, we have said that $frac{X_n}{ln(n)}geq 1$ is true for infinitely many $n$.

Why is that true? Is this fact connected with the case $alpha leq 1$?










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    1












    $begingroup$


    Given the random variable $X_n$, to be exponential distributed with parameter $1$, we define
    $$A_n:=left{X_n>alpha ln(n)right}.$$
    We've shown in the classes that for $alpha leq 1$, $A_n$ occurs infinitely times, and for $alpha>1$ finitely times. Now calculating the limes superior $overline{lim}_{nrightarrowinfty}frac{X_n}{ln(n)}$, we have said that $frac{X_n}{ln(n)}geq 1$ is true for infinitely many $n$.

    Why is that true? Is this fact connected with the case $alpha leq 1$?










    share|cite|improve this question











    $endgroup$















      1












      1








      1





      $begingroup$


      Given the random variable $X_n$, to be exponential distributed with parameter $1$, we define
      $$A_n:=left{X_n>alpha ln(n)right}.$$
      We've shown in the classes that for $alpha leq 1$, $A_n$ occurs infinitely times, and for $alpha>1$ finitely times. Now calculating the limes superior $overline{lim}_{nrightarrowinfty}frac{X_n}{ln(n)}$, we have said that $frac{X_n}{ln(n)}geq 1$ is true for infinitely many $n$.

      Why is that true? Is this fact connected with the case $alpha leq 1$?










      share|cite|improve this question











      $endgroup$




      Given the random variable $X_n$, to be exponential distributed with parameter $1$, we define
      $$A_n:=left{X_n>alpha ln(n)right}.$$
      We've shown in the classes that for $alpha leq 1$, $A_n$ occurs infinitely times, and for $alpha>1$ finitely times. Now calculating the limes superior $overline{lim}_{nrightarrowinfty}frac{X_n}{ln(n)}$, we have said that $frac{X_n}{ln(n)}geq 1$ is true for infinitely many $n$.

      Why is that true? Is this fact connected with the case $alpha leq 1$?







      probability-theory convergence limsup-and-liminf exponential-distribution






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      edited Dec 10 '18 at 20:50









      user376343

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      3,3532825










      asked Dec 3 '18 at 9:52









      ThesinusThesinus

      247210




      247210






















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          $begingroup$

          $P(X_n >alpha log, n) =int_{alpha log, n}^{infty} e^{-x}, dx=frac 1 {n^{alpha}}$. Assuming independence of $X_n$'s we can conclude from Borel Cantelli Lemma and convergence of $sum frac 1 {n^{alpha}}$ that $X_n leq alpha log, n$ for all $n$ sufficently large with probability $1$ if $alpha >1$. If $alpha leq 1$ the same argument shows that $X_n >alpha log, n$ for inifintely many $n$ with probability $1$. This implies that $lim sup frac {X_n} {log, n} geq 1$ with probability $1$.






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            $begingroup$

            $P(X_n >alpha log, n) =int_{alpha log, n}^{infty} e^{-x}, dx=frac 1 {n^{alpha}}$. Assuming independence of $X_n$'s we can conclude from Borel Cantelli Lemma and convergence of $sum frac 1 {n^{alpha}}$ that $X_n leq alpha log, n$ for all $n$ sufficently large with probability $1$ if $alpha >1$. If $alpha leq 1$ the same argument shows that $X_n >alpha log, n$ for inifintely many $n$ with probability $1$. This implies that $lim sup frac {X_n} {log, n} geq 1$ with probability $1$.






            share|cite|improve this answer











            $endgroup$


















              1












              $begingroup$

              $P(X_n >alpha log, n) =int_{alpha log, n}^{infty} e^{-x}, dx=frac 1 {n^{alpha}}$. Assuming independence of $X_n$'s we can conclude from Borel Cantelli Lemma and convergence of $sum frac 1 {n^{alpha}}$ that $X_n leq alpha log, n$ for all $n$ sufficently large with probability $1$ if $alpha >1$. If $alpha leq 1$ the same argument shows that $X_n >alpha log, n$ for inifintely many $n$ with probability $1$. This implies that $lim sup frac {X_n} {log, n} geq 1$ with probability $1$.






              share|cite|improve this answer











              $endgroup$
















                1












                1








                1





                $begingroup$

                $P(X_n >alpha log, n) =int_{alpha log, n}^{infty} e^{-x}, dx=frac 1 {n^{alpha}}$. Assuming independence of $X_n$'s we can conclude from Borel Cantelli Lemma and convergence of $sum frac 1 {n^{alpha}}$ that $X_n leq alpha log, n$ for all $n$ sufficently large with probability $1$ if $alpha >1$. If $alpha leq 1$ the same argument shows that $X_n >alpha log, n$ for inifintely many $n$ with probability $1$. This implies that $lim sup frac {X_n} {log, n} geq 1$ with probability $1$.






                share|cite|improve this answer











                $endgroup$



                $P(X_n >alpha log, n) =int_{alpha log, n}^{infty} e^{-x}, dx=frac 1 {n^{alpha}}$. Assuming independence of $X_n$'s we can conclude from Borel Cantelli Lemma and convergence of $sum frac 1 {n^{alpha}}$ that $X_n leq alpha log, n$ for all $n$ sufficently large with probability $1$ if $alpha >1$. If $alpha leq 1$ the same argument shows that $X_n >alpha log, n$ for inifintely many $n$ with probability $1$. This implies that $lim sup frac {X_n} {log, n} geq 1$ with probability $1$.







                share|cite|improve this answer














                share|cite|improve this answer



                share|cite|improve this answer








                edited Dec 3 '18 at 10:06

























                answered Dec 3 '18 at 9:59









                Kavi Rama MurthyKavi Rama Murthy

                53.8k32055




                53.8k32055






























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