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Find n from summation


Find the original function in a summationSummation of $i cdot j$ from $ 1$ to$ 3$Evaluating Summation of $5^-n$ from $n=4$ to infinityExtract a variable from the following summationCalculating summation on integer numbers from $-infty$ to $infty$Order of growth from summationHow to solve this summation derived from an algorithm?M/G/1 queue: difference between $p_o$ and $p(0)$?How to find closed form of summationProof of identity about generalized binomial sequences.













1












$begingroup$


I ran into this expression while reading through a chapter a book:



$$sum_i=0^nfrace^-15001500^ii! ge 0.95$$



And they solve for $n$ and got $n = 1564$ from the expression, but there's no detail on how to get $n$. Can someone explain how to get that number for $n$?



The book is Discrete Event System Simulation by Jerry Banks. This is in the 5th Edition, Chapter 6 Example 6.15, if anyone wants to look this up.










share|cite|improve this question











$endgroup$











  • $begingroup$
    Is it possible the author used Mathematica (or some other mathematical software) to determine $n$? I can offer one or two techniques to solve for some such $n$, but I'm not sure anything is quite as tight as $n=1564$.
    $endgroup$
    – Clayton
    yesterday










  • $begingroup$
    That might have been the case. I tried to crunch this in wolfram alpha and couldn't get the answer.
    $endgroup$
    – PTN
    yesterday






  • 3




    $begingroup$
    The Poisson probability distribution for a mean of 1500 will be approximately a normal distribution. The probability to be 1.64485 sigma above the mean is 5% for a normal distribution, therefore you would roughly estimate n to be $1500 + 1.64485 sqrt1500approx 1564$
    $endgroup$
    – Count Iblis
    yesterday











  • $begingroup$
    @CountIblis That makes sense!
    $endgroup$
    – PTN
    yesterday















1












$begingroup$


I ran into this expression while reading through a chapter a book:



$$sum_i=0^nfrace^-15001500^ii! ge 0.95$$



And they solve for $n$ and got $n = 1564$ from the expression, but there's no detail on how to get $n$. Can someone explain how to get that number for $n$?



The book is Discrete Event System Simulation by Jerry Banks. This is in the 5th Edition, Chapter 6 Example 6.15, if anyone wants to look this up.










share|cite|improve this question











$endgroup$











  • $begingroup$
    Is it possible the author used Mathematica (or some other mathematical software) to determine $n$? I can offer one or two techniques to solve for some such $n$, but I'm not sure anything is quite as tight as $n=1564$.
    $endgroup$
    – Clayton
    yesterday










  • $begingroup$
    That might have been the case. I tried to crunch this in wolfram alpha and couldn't get the answer.
    $endgroup$
    – PTN
    yesterday






  • 3




    $begingroup$
    The Poisson probability distribution for a mean of 1500 will be approximately a normal distribution. The probability to be 1.64485 sigma above the mean is 5% for a normal distribution, therefore you would roughly estimate n to be $1500 + 1.64485 sqrt1500approx 1564$
    $endgroup$
    – Count Iblis
    yesterday











  • $begingroup$
    @CountIblis That makes sense!
    $endgroup$
    – PTN
    yesterday













1












1








1





$begingroup$


I ran into this expression while reading through a chapter a book:



$$sum_i=0^nfrace^-15001500^ii! ge 0.95$$



And they solve for $n$ and got $n = 1564$ from the expression, but there's no detail on how to get $n$. Can someone explain how to get that number for $n$?



The book is Discrete Event System Simulation by Jerry Banks. This is in the 5th Edition, Chapter 6 Example 6.15, if anyone wants to look this up.










share|cite|improve this question











$endgroup$




I ran into this expression while reading through a chapter a book:



$$sum_i=0^nfrace^-15001500^ii! ge 0.95$$



And they solve for $n$ and got $n = 1564$ from the expression, but there's no detail on how to get $n$. Can someone explain how to get that number for $n$?



The book is Discrete Event System Simulation by Jerry Banks. This is in the 5th Edition, Chapter 6 Example 6.15, if anyone wants to look this up.







summation poisson-distribution






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited yesterday







PTN

















asked yesterday









PTNPTN

1496




1496











  • $begingroup$
    Is it possible the author used Mathematica (or some other mathematical software) to determine $n$? I can offer one or two techniques to solve for some such $n$, but I'm not sure anything is quite as tight as $n=1564$.
    $endgroup$
    – Clayton
    yesterday










  • $begingroup$
    That might have been the case. I tried to crunch this in wolfram alpha and couldn't get the answer.
    $endgroup$
    – PTN
    yesterday






  • 3




    $begingroup$
    The Poisson probability distribution for a mean of 1500 will be approximately a normal distribution. The probability to be 1.64485 sigma above the mean is 5% for a normal distribution, therefore you would roughly estimate n to be $1500 + 1.64485 sqrt1500approx 1564$
    $endgroup$
    – Count Iblis
    yesterday











  • $begingroup$
    @CountIblis That makes sense!
    $endgroup$
    – PTN
    yesterday
















  • $begingroup$
    Is it possible the author used Mathematica (or some other mathematical software) to determine $n$? I can offer one or two techniques to solve for some such $n$, but I'm not sure anything is quite as tight as $n=1564$.
    $endgroup$
    – Clayton
    yesterday










  • $begingroup$
    That might have been the case. I tried to crunch this in wolfram alpha and couldn't get the answer.
    $endgroup$
    – PTN
    yesterday






  • 3




    $begingroup$
    The Poisson probability distribution for a mean of 1500 will be approximately a normal distribution. The probability to be 1.64485 sigma above the mean is 5% for a normal distribution, therefore you would roughly estimate n to be $1500 + 1.64485 sqrt1500approx 1564$
    $endgroup$
    – Count Iblis
    yesterday











  • $begingroup$
    @CountIblis That makes sense!
    $endgroup$
    – PTN
    yesterday















$begingroup$
Is it possible the author used Mathematica (or some other mathematical software) to determine $n$? I can offer one or two techniques to solve for some such $n$, but I'm not sure anything is quite as tight as $n=1564$.
$endgroup$
– Clayton
yesterday




$begingroup$
Is it possible the author used Mathematica (or some other mathematical software) to determine $n$? I can offer one or two techniques to solve for some such $n$, but I'm not sure anything is quite as tight as $n=1564$.
$endgroup$
– Clayton
yesterday












$begingroup$
That might have been the case. I tried to crunch this in wolfram alpha and couldn't get the answer.
$endgroup$
– PTN
yesterday




$begingroup$
That might have been the case. I tried to crunch this in wolfram alpha and couldn't get the answer.
$endgroup$
– PTN
yesterday




3




3




$begingroup$
The Poisson probability distribution for a mean of 1500 will be approximately a normal distribution. The probability to be 1.64485 sigma above the mean is 5% for a normal distribution, therefore you would roughly estimate n to be $1500 + 1.64485 sqrt1500approx 1564$
$endgroup$
– Count Iblis
yesterday





$begingroup$
The Poisson probability distribution for a mean of 1500 will be approximately a normal distribution. The probability to be 1.64485 sigma above the mean is 5% for a normal distribution, therefore you would roughly estimate n to be $1500 + 1.64485 sqrt1500approx 1564$
$endgroup$
– Count Iblis
yesterday













$begingroup$
@CountIblis That makes sense!
$endgroup$
– PTN
yesterday




$begingroup$
@CountIblis That makes sense!
$endgroup$
– PTN
yesterday










2 Answers
2






active

oldest

votes


















2












$begingroup$

The probability distribution is the Poisson distribution with $lambda=1500$. For large $lambda$ the distribution is approximately normal with mean $lambda$ and variance $lambda$, so standard deviation $sigma=sqrt lambda$. For a one-sided normal distribution you have $5%$ of the area above mean + $1.648 sigma$, which here is $1500+1.648 sqrt 1500 approx 1564$






share|cite|improve this answer









$endgroup$




















    1












    $begingroup$

    From a purely algebraic point of view
    $$sum_i=0^nfrace^-15001500^ii! =fracGamma (n+1,1500)Gamma (n+1)$$ So, you could consider that we look for the zero of function
    $$f(x)=fracGamma (x+1,1500)Gamma (x+1)-0.95$$ which is not very well conditioned. Better will be to search for the zero of
    $$g(x)=log left(fracGamma (x+1,1500)Gamma (x+1)right)-log(0.95)$$ Remembering that
    $fracGamma (m,m)Gamma (m) < frac 12$, let us use Newton method with $x_0=1500$. Since $g(x_0) <0$ and $g''(x_0) <0$, by Darboux theorem, we shall not face any overshoot of the solution which is $x=1563.485020$.



    Just for the fun of it, ask Wolfram Alpha to plot $g(x)$ for $1500 leq x leq 1600$.






    share|cite|improve this answer









    $endgroup$












      Your Answer





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      2 Answers
      2






      active

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      2 Answers
      2






      active

      oldest

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      active

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      active

      oldest

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      2












      $begingroup$

      The probability distribution is the Poisson distribution with $lambda=1500$. For large $lambda$ the distribution is approximately normal with mean $lambda$ and variance $lambda$, so standard deviation $sigma=sqrt lambda$. For a one-sided normal distribution you have $5%$ of the area above mean + $1.648 sigma$, which here is $1500+1.648 sqrt 1500 approx 1564$






      share|cite|improve this answer









      $endgroup$

















        2












        $begingroup$

        The probability distribution is the Poisson distribution with $lambda=1500$. For large $lambda$ the distribution is approximately normal with mean $lambda$ and variance $lambda$, so standard deviation $sigma=sqrt lambda$. For a one-sided normal distribution you have $5%$ of the area above mean + $1.648 sigma$, which here is $1500+1.648 sqrt 1500 approx 1564$






        share|cite|improve this answer









        $endgroup$















          2












          2








          2





          $begingroup$

          The probability distribution is the Poisson distribution with $lambda=1500$. For large $lambda$ the distribution is approximately normal with mean $lambda$ and variance $lambda$, so standard deviation $sigma=sqrt lambda$. For a one-sided normal distribution you have $5%$ of the area above mean + $1.648 sigma$, which here is $1500+1.648 sqrt 1500 approx 1564$






          share|cite|improve this answer









          $endgroup$



          The probability distribution is the Poisson distribution with $lambda=1500$. For large $lambda$ the distribution is approximately normal with mean $lambda$ and variance $lambda$, so standard deviation $sigma=sqrt lambda$. For a one-sided normal distribution you have $5%$ of the area above mean + $1.648 sigma$, which here is $1500+1.648 sqrt 1500 approx 1564$







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered yesterday









          Ross MillikanRoss Millikan

          300k24200375




          300k24200375





















              1












              $begingroup$

              From a purely algebraic point of view
              $$sum_i=0^nfrace^-15001500^ii! =fracGamma (n+1,1500)Gamma (n+1)$$ So, you could consider that we look for the zero of function
              $$f(x)=fracGamma (x+1,1500)Gamma (x+1)-0.95$$ which is not very well conditioned. Better will be to search for the zero of
              $$g(x)=log left(fracGamma (x+1,1500)Gamma (x+1)right)-log(0.95)$$ Remembering that
              $fracGamma (m,m)Gamma (m) < frac 12$, let us use Newton method with $x_0=1500$. Since $g(x_0) <0$ and $g''(x_0) <0$, by Darboux theorem, we shall not face any overshoot of the solution which is $x=1563.485020$.



              Just for the fun of it, ask Wolfram Alpha to plot $g(x)$ for $1500 leq x leq 1600$.






              share|cite|improve this answer









              $endgroup$

















                1












                $begingroup$

                From a purely algebraic point of view
                $$sum_i=0^nfrace^-15001500^ii! =fracGamma (n+1,1500)Gamma (n+1)$$ So, you could consider that we look for the zero of function
                $$f(x)=fracGamma (x+1,1500)Gamma (x+1)-0.95$$ which is not very well conditioned. Better will be to search for the zero of
                $$g(x)=log left(fracGamma (x+1,1500)Gamma (x+1)right)-log(0.95)$$ Remembering that
                $fracGamma (m,m)Gamma (m) < frac 12$, let us use Newton method with $x_0=1500$. Since $g(x_0) <0$ and $g''(x_0) <0$, by Darboux theorem, we shall not face any overshoot of the solution which is $x=1563.485020$.



                Just for the fun of it, ask Wolfram Alpha to plot $g(x)$ for $1500 leq x leq 1600$.






                share|cite|improve this answer









                $endgroup$















                  1












                  1








                  1





                  $begingroup$

                  From a purely algebraic point of view
                  $$sum_i=0^nfrace^-15001500^ii! =fracGamma (n+1,1500)Gamma (n+1)$$ So, you could consider that we look for the zero of function
                  $$f(x)=fracGamma (x+1,1500)Gamma (x+1)-0.95$$ which is not very well conditioned. Better will be to search for the zero of
                  $$g(x)=log left(fracGamma (x+1,1500)Gamma (x+1)right)-log(0.95)$$ Remembering that
                  $fracGamma (m,m)Gamma (m) < frac 12$, let us use Newton method with $x_0=1500$. Since $g(x_0) <0$ and $g''(x_0) <0$, by Darboux theorem, we shall not face any overshoot of the solution which is $x=1563.485020$.



                  Just for the fun of it, ask Wolfram Alpha to plot $g(x)$ for $1500 leq x leq 1600$.






                  share|cite|improve this answer









                  $endgroup$



                  From a purely algebraic point of view
                  $$sum_i=0^nfrace^-15001500^ii! =fracGamma (n+1,1500)Gamma (n+1)$$ So, you could consider that we look for the zero of function
                  $$f(x)=fracGamma (x+1,1500)Gamma (x+1)-0.95$$ which is not very well conditioned. Better will be to search for the zero of
                  $$g(x)=log left(fracGamma (x+1,1500)Gamma (x+1)right)-log(0.95)$$ Remembering that
                  $fracGamma (m,m)Gamma (m) < frac 12$, let us use Newton method with $x_0=1500$. Since $g(x_0) <0$ and $g''(x_0) <0$, by Darboux theorem, we shall not face any overshoot of the solution which is $x=1563.485020$.



                  Just for the fun of it, ask Wolfram Alpha to plot $g(x)$ for $1500 leq x leq 1600$.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered 21 hours ago









                  Claude LeiboviciClaude Leibovici

                  125k1158135




                  125k1158135



























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