Urns, balls, and simplifying an infinite series
$begingroup$
Consider a large number of urns and a large number of people each randomly placing $n sim Poisson(lambda)$ balls in urns (people do not place multiple balls in the same urn). Urns receiving multiple balls pick a ball at random. If an individual's balls are chosen by multiple urns, then the individual randomly chooses an urn and we call that a match. Letting z denote the probability that person i is chosen by urn j, conditional on placing a ball in j, I conjecture that the probability that an urn that has chosen a ball forms a match with that ball is given by:
$$displaystylesum_{ngeq 1} left( frac{lambda^ne^{-lambda}}{n!} right)left[sum_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]$$
Simplifying the expression inside of the brackets yields
$$ frac{(1-z)^{n-1}}{n} sum_{k=0}^{n-1}
{n choose k+1}left( frac{z}{1-z} right)^k $$
This is close to a familiar looking series for the inner brackets, but I'm not sure how to proceed. Any suggestions or references?
probability sequences-and-series
$endgroup$
add a comment |
$begingroup$
Consider a large number of urns and a large number of people each randomly placing $n sim Poisson(lambda)$ balls in urns (people do not place multiple balls in the same urn). Urns receiving multiple balls pick a ball at random. If an individual's balls are chosen by multiple urns, then the individual randomly chooses an urn and we call that a match. Letting z denote the probability that person i is chosen by urn j, conditional on placing a ball in j, I conjecture that the probability that an urn that has chosen a ball forms a match with that ball is given by:
$$displaystylesum_{ngeq 1} left( frac{lambda^ne^{-lambda}}{n!} right)left[sum_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]$$
Simplifying the expression inside of the brackets yields
$$ frac{(1-z)^{n-1}}{n} sum_{k=0}^{n-1}
{n choose k+1}left( frac{z}{1-z} right)^k $$
This is close to a familiar looking series for the inner brackets, but I'm not sure how to proceed. Any suggestions or references?
probability sequences-and-series
$endgroup$
add a comment |
$begingroup$
Consider a large number of urns and a large number of people each randomly placing $n sim Poisson(lambda)$ balls in urns (people do not place multiple balls in the same urn). Urns receiving multiple balls pick a ball at random. If an individual's balls are chosen by multiple urns, then the individual randomly chooses an urn and we call that a match. Letting z denote the probability that person i is chosen by urn j, conditional on placing a ball in j, I conjecture that the probability that an urn that has chosen a ball forms a match with that ball is given by:
$$displaystylesum_{ngeq 1} left( frac{lambda^ne^{-lambda}}{n!} right)left[sum_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]$$
Simplifying the expression inside of the brackets yields
$$ frac{(1-z)^{n-1}}{n} sum_{k=0}^{n-1}
{n choose k+1}left( frac{z}{1-z} right)^k $$
This is close to a familiar looking series for the inner brackets, but I'm not sure how to proceed. Any suggestions or references?
probability sequences-and-series
$endgroup$
Consider a large number of urns and a large number of people each randomly placing $n sim Poisson(lambda)$ balls in urns (people do not place multiple balls in the same urn). Urns receiving multiple balls pick a ball at random. If an individual's balls are chosen by multiple urns, then the individual randomly chooses an urn and we call that a match. Letting z denote the probability that person i is chosen by urn j, conditional on placing a ball in j, I conjecture that the probability that an urn that has chosen a ball forms a match with that ball is given by:
$$displaystylesum_{ngeq 1} left( frac{lambda^ne^{-lambda}}{n!} right)left[sum_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]$$
Simplifying the expression inside of the brackets yields
$$ frac{(1-z)^{n-1}}{n} sum_{k=0}^{n-1}
{n choose k+1}left( frac{z}{1-z} right)^k $$
This is close to a familiar looking series for the inner brackets, but I'm not sure how to proceed. Any suggestions or references?
probability sequences-and-series
probability sequences-and-series
edited Jan 26 at 0:11
Math1000
19.3k31745
19.3k31745
asked Jan 25 at 23:17
JohnJohn
255
255
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
Simplifying the expression inside of the brackets:
$left[sumlimits_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]tag1$
Using the fact that $frac{1}{k+1}=intlimits_0^1 t^kdt$ and replace the order the sum and integral we get:
$intlimits_0^1sumlimits_{k=0}^{n-1} {n-1choose k} (zt)^k(1-z)^{n-1-k}dttag2$
According to Binomial formula we can write:
$intlimits_0^1 (zt+1-z)^{n-1}dt=[frac{(zt+1-z)^n}{zn}]_{t=0}^1=frac{1}{zn}-frac{(1-z)^n}{zn}tag3$
So the result of the sum inside the brakets is:
$frac{1}{zn}-frac{(1-z)^n}{zn}tag4$
Regarding the whole expression:
$sumlimits_{n=1}^infty frac{lambda^ne^{-lambda}}{n!}big(frac{1}{zn}-frac{(1-z)^n}{zn}big)tag5$
Using the same trick as in (2) we have:
$frac{e^{-lambda}}{z}intlimits_0^1 frac{1}{t}sumlimits_{n=1}^infty frac{lambda^n}{n!}big(t^n-t^n(1-z)^nbig)tag6$
Known that $sumlimits_{n=1}^infty frac{x^n}{n!}=sumlimits_{n=0}^infty frac{x^n}{n!}-1;$ we can form the(5) in the following way:
$frac{e^{-lambda}}{z}intlimits_0^1 big(frac{e^{lambda t}}{t}-frac{e^{lambda t(1-z)}}{t}big)dt tag7$
This integral can be solved by using the integral functions.
$endgroup$
1
$begingroup$
This is a nice solution, for sure. I did not work the problem but I wonder if, once the expression inside brackets has been fully simplified (this eliminates the summation over $k$), we could not do the same using the complete and incomplte gamma functions. By the way, $+1$. Cheers.
$endgroup$
– Claude Leibovici
Jan 26 at 5:40
1
$begingroup$
@Claude Leibovici, Thank you, and regards.
$endgroup$
– JV.Stalker
Jan 26 at 6:35
$begingroup$
@JV.Stalker Thanks so much. Can you explain what you mean when you write "this integral can be solved by using the integral functions"? Also, I presume this cannot be expressed in terms of elementary functions, but is there an approximation that can? Thanks again.
$endgroup$
– John
Jan 26 at 16:04
$begingroup$
@John, Sorry I leave out the "exponential" expression from my sentence. Accordace with Wolfram Alpha the last integral equal to: $frac{e^{-lambda}}{z}big(Ei(lambda t)-Ei(lambda t(z-1))big)|_0^1=frac{e^{-lambda}}{z}Big(ln(1-z)+Gamma(0,lambda(z-1))-Gamma(0,lambda)Big)$ what was seen by Claude Leibovici in advance. The approximation could be a nother exercise, I start to learn this topic. Best regards,
$endgroup$
– JV.Stalker
Jan 27 at 5:15
add a comment |
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$begingroup$
Simplifying the expression inside of the brackets:
$left[sumlimits_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]tag1$
Using the fact that $frac{1}{k+1}=intlimits_0^1 t^kdt$ and replace the order the sum and integral we get:
$intlimits_0^1sumlimits_{k=0}^{n-1} {n-1choose k} (zt)^k(1-z)^{n-1-k}dttag2$
According to Binomial formula we can write:
$intlimits_0^1 (zt+1-z)^{n-1}dt=[frac{(zt+1-z)^n}{zn}]_{t=0}^1=frac{1}{zn}-frac{(1-z)^n}{zn}tag3$
So the result of the sum inside the brakets is:
$frac{1}{zn}-frac{(1-z)^n}{zn}tag4$
Regarding the whole expression:
$sumlimits_{n=1}^infty frac{lambda^ne^{-lambda}}{n!}big(frac{1}{zn}-frac{(1-z)^n}{zn}big)tag5$
Using the same trick as in (2) we have:
$frac{e^{-lambda}}{z}intlimits_0^1 frac{1}{t}sumlimits_{n=1}^infty frac{lambda^n}{n!}big(t^n-t^n(1-z)^nbig)tag6$
Known that $sumlimits_{n=1}^infty frac{x^n}{n!}=sumlimits_{n=0}^infty frac{x^n}{n!}-1;$ we can form the(5) in the following way:
$frac{e^{-lambda}}{z}intlimits_0^1 big(frac{e^{lambda t}}{t}-frac{e^{lambda t(1-z)}}{t}big)dt tag7$
This integral can be solved by using the integral functions.
$endgroup$
1
$begingroup$
This is a nice solution, for sure. I did not work the problem but I wonder if, once the expression inside brackets has been fully simplified (this eliminates the summation over $k$), we could not do the same using the complete and incomplte gamma functions. By the way, $+1$. Cheers.
$endgroup$
– Claude Leibovici
Jan 26 at 5:40
1
$begingroup$
@Claude Leibovici, Thank you, and regards.
$endgroup$
– JV.Stalker
Jan 26 at 6:35
$begingroup$
@JV.Stalker Thanks so much. Can you explain what you mean when you write "this integral can be solved by using the integral functions"? Also, I presume this cannot be expressed in terms of elementary functions, but is there an approximation that can? Thanks again.
$endgroup$
– John
Jan 26 at 16:04
$begingroup$
@John, Sorry I leave out the "exponential" expression from my sentence. Accordace with Wolfram Alpha the last integral equal to: $frac{e^{-lambda}}{z}big(Ei(lambda t)-Ei(lambda t(z-1))big)|_0^1=frac{e^{-lambda}}{z}Big(ln(1-z)+Gamma(0,lambda(z-1))-Gamma(0,lambda)Big)$ what was seen by Claude Leibovici in advance. The approximation could be a nother exercise, I start to learn this topic. Best regards,
$endgroup$
– JV.Stalker
Jan 27 at 5:15
add a comment |
$begingroup$
Simplifying the expression inside of the brackets:
$left[sumlimits_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]tag1$
Using the fact that $frac{1}{k+1}=intlimits_0^1 t^kdt$ and replace the order the sum and integral we get:
$intlimits_0^1sumlimits_{k=0}^{n-1} {n-1choose k} (zt)^k(1-z)^{n-1-k}dttag2$
According to Binomial formula we can write:
$intlimits_0^1 (zt+1-z)^{n-1}dt=[frac{(zt+1-z)^n}{zn}]_{t=0}^1=frac{1}{zn}-frac{(1-z)^n}{zn}tag3$
So the result of the sum inside the brakets is:
$frac{1}{zn}-frac{(1-z)^n}{zn}tag4$
Regarding the whole expression:
$sumlimits_{n=1}^infty frac{lambda^ne^{-lambda}}{n!}big(frac{1}{zn}-frac{(1-z)^n}{zn}big)tag5$
Using the same trick as in (2) we have:
$frac{e^{-lambda}}{z}intlimits_0^1 frac{1}{t}sumlimits_{n=1}^infty frac{lambda^n}{n!}big(t^n-t^n(1-z)^nbig)tag6$
Known that $sumlimits_{n=1}^infty frac{x^n}{n!}=sumlimits_{n=0}^infty frac{x^n}{n!}-1;$ we can form the(5) in the following way:
$frac{e^{-lambda}}{z}intlimits_0^1 big(frac{e^{lambda t}}{t}-frac{e^{lambda t(1-z)}}{t}big)dt tag7$
This integral can be solved by using the integral functions.
$endgroup$
1
$begingroup$
This is a nice solution, for sure. I did not work the problem but I wonder if, once the expression inside brackets has been fully simplified (this eliminates the summation over $k$), we could not do the same using the complete and incomplte gamma functions. By the way, $+1$. Cheers.
$endgroup$
– Claude Leibovici
Jan 26 at 5:40
1
$begingroup$
@Claude Leibovici, Thank you, and regards.
$endgroup$
– JV.Stalker
Jan 26 at 6:35
$begingroup$
@JV.Stalker Thanks so much. Can you explain what you mean when you write "this integral can be solved by using the integral functions"? Also, I presume this cannot be expressed in terms of elementary functions, but is there an approximation that can? Thanks again.
$endgroup$
– John
Jan 26 at 16:04
$begingroup$
@John, Sorry I leave out the "exponential" expression from my sentence. Accordace with Wolfram Alpha the last integral equal to: $frac{e^{-lambda}}{z}big(Ei(lambda t)-Ei(lambda t(z-1))big)|_0^1=frac{e^{-lambda}}{z}Big(ln(1-z)+Gamma(0,lambda(z-1))-Gamma(0,lambda)Big)$ what was seen by Claude Leibovici in advance. The approximation could be a nother exercise, I start to learn this topic. Best regards,
$endgroup$
– JV.Stalker
Jan 27 at 5:15
add a comment |
$begingroup$
Simplifying the expression inside of the brackets:
$left[sumlimits_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]tag1$
Using the fact that $frac{1}{k+1}=intlimits_0^1 t^kdt$ and replace the order the sum and integral we get:
$intlimits_0^1sumlimits_{k=0}^{n-1} {n-1choose k} (zt)^k(1-z)^{n-1-k}dttag2$
According to Binomial formula we can write:
$intlimits_0^1 (zt+1-z)^{n-1}dt=[frac{(zt+1-z)^n}{zn}]_{t=0}^1=frac{1}{zn}-frac{(1-z)^n}{zn}tag3$
So the result of the sum inside the brakets is:
$frac{1}{zn}-frac{(1-z)^n}{zn}tag4$
Regarding the whole expression:
$sumlimits_{n=1}^infty frac{lambda^ne^{-lambda}}{n!}big(frac{1}{zn}-frac{(1-z)^n}{zn}big)tag5$
Using the same trick as in (2) we have:
$frac{e^{-lambda}}{z}intlimits_0^1 frac{1}{t}sumlimits_{n=1}^infty frac{lambda^n}{n!}big(t^n-t^n(1-z)^nbig)tag6$
Known that $sumlimits_{n=1}^infty frac{x^n}{n!}=sumlimits_{n=0}^infty frac{x^n}{n!}-1;$ we can form the(5) in the following way:
$frac{e^{-lambda}}{z}intlimits_0^1 big(frac{e^{lambda t}}{t}-frac{e^{lambda t(1-z)}}{t}big)dt tag7$
This integral can be solved by using the integral functions.
$endgroup$
Simplifying the expression inside of the brackets:
$left[sumlimits_{k=0}^{n-1} {n-1choose k} z^k(1-z)^{n-1-k}left(frac{1}{k+1} right) right]tag1$
Using the fact that $frac{1}{k+1}=intlimits_0^1 t^kdt$ and replace the order the sum and integral we get:
$intlimits_0^1sumlimits_{k=0}^{n-1} {n-1choose k} (zt)^k(1-z)^{n-1-k}dttag2$
According to Binomial formula we can write:
$intlimits_0^1 (zt+1-z)^{n-1}dt=[frac{(zt+1-z)^n}{zn}]_{t=0}^1=frac{1}{zn}-frac{(1-z)^n}{zn}tag3$
So the result of the sum inside the brakets is:
$frac{1}{zn}-frac{(1-z)^n}{zn}tag4$
Regarding the whole expression:
$sumlimits_{n=1}^infty frac{lambda^ne^{-lambda}}{n!}big(frac{1}{zn}-frac{(1-z)^n}{zn}big)tag5$
Using the same trick as in (2) we have:
$frac{e^{-lambda}}{z}intlimits_0^1 frac{1}{t}sumlimits_{n=1}^infty frac{lambda^n}{n!}big(t^n-t^n(1-z)^nbig)tag6$
Known that $sumlimits_{n=1}^infty frac{x^n}{n!}=sumlimits_{n=0}^infty frac{x^n}{n!}-1;$ we can form the(5) in the following way:
$frac{e^{-lambda}}{z}intlimits_0^1 big(frac{e^{lambda t}}{t}-frac{e^{lambda t(1-z)}}{t}big)dt tag7$
This integral can be solved by using the integral functions.
answered Jan 26 at 5:02
JV.StalkerJV.Stalker
93149
93149
1
$begingroup$
This is a nice solution, for sure. I did not work the problem but I wonder if, once the expression inside brackets has been fully simplified (this eliminates the summation over $k$), we could not do the same using the complete and incomplte gamma functions. By the way, $+1$. Cheers.
$endgroup$
– Claude Leibovici
Jan 26 at 5:40
1
$begingroup$
@Claude Leibovici, Thank you, and regards.
$endgroup$
– JV.Stalker
Jan 26 at 6:35
$begingroup$
@JV.Stalker Thanks so much. Can you explain what you mean when you write "this integral can be solved by using the integral functions"? Also, I presume this cannot be expressed in terms of elementary functions, but is there an approximation that can? Thanks again.
$endgroup$
– John
Jan 26 at 16:04
$begingroup$
@John, Sorry I leave out the "exponential" expression from my sentence. Accordace with Wolfram Alpha the last integral equal to: $frac{e^{-lambda}}{z}big(Ei(lambda t)-Ei(lambda t(z-1))big)|_0^1=frac{e^{-lambda}}{z}Big(ln(1-z)+Gamma(0,lambda(z-1))-Gamma(0,lambda)Big)$ what was seen by Claude Leibovici in advance. The approximation could be a nother exercise, I start to learn this topic. Best regards,
$endgroup$
– JV.Stalker
Jan 27 at 5:15
add a comment |
1
$begingroup$
This is a nice solution, for sure. I did not work the problem but I wonder if, once the expression inside brackets has been fully simplified (this eliminates the summation over $k$), we could not do the same using the complete and incomplte gamma functions. By the way, $+1$. Cheers.
$endgroup$
– Claude Leibovici
Jan 26 at 5:40
1
$begingroup$
@Claude Leibovici, Thank you, and regards.
$endgroup$
– JV.Stalker
Jan 26 at 6:35
$begingroup$
@JV.Stalker Thanks so much. Can you explain what you mean when you write "this integral can be solved by using the integral functions"? Also, I presume this cannot be expressed in terms of elementary functions, but is there an approximation that can? Thanks again.
$endgroup$
– John
Jan 26 at 16:04
$begingroup$
@John, Sorry I leave out the "exponential" expression from my sentence. Accordace with Wolfram Alpha the last integral equal to: $frac{e^{-lambda}}{z}big(Ei(lambda t)-Ei(lambda t(z-1))big)|_0^1=frac{e^{-lambda}}{z}Big(ln(1-z)+Gamma(0,lambda(z-1))-Gamma(0,lambda)Big)$ what was seen by Claude Leibovici in advance. The approximation could be a nother exercise, I start to learn this topic. Best regards,
$endgroup$
– JV.Stalker
Jan 27 at 5:15
1
1
$begingroup$
This is a nice solution, for sure. I did not work the problem but I wonder if, once the expression inside brackets has been fully simplified (this eliminates the summation over $k$), we could not do the same using the complete and incomplte gamma functions. By the way, $+1$. Cheers.
$endgroup$
– Claude Leibovici
Jan 26 at 5:40
$begingroup$
This is a nice solution, for sure. I did not work the problem but I wonder if, once the expression inside brackets has been fully simplified (this eliminates the summation over $k$), we could not do the same using the complete and incomplte gamma functions. By the way, $+1$. Cheers.
$endgroup$
– Claude Leibovici
Jan 26 at 5:40
1
1
$begingroup$
@Claude Leibovici, Thank you, and regards.
$endgroup$
– JV.Stalker
Jan 26 at 6:35
$begingroup$
@Claude Leibovici, Thank you, and regards.
$endgroup$
– JV.Stalker
Jan 26 at 6:35
$begingroup$
@JV.Stalker Thanks so much. Can you explain what you mean when you write "this integral can be solved by using the integral functions"? Also, I presume this cannot be expressed in terms of elementary functions, but is there an approximation that can? Thanks again.
$endgroup$
– John
Jan 26 at 16:04
$begingroup$
@JV.Stalker Thanks so much. Can you explain what you mean when you write "this integral can be solved by using the integral functions"? Also, I presume this cannot be expressed in terms of elementary functions, but is there an approximation that can? Thanks again.
$endgroup$
– John
Jan 26 at 16:04
$begingroup$
@John, Sorry I leave out the "exponential" expression from my sentence. Accordace with Wolfram Alpha the last integral equal to: $frac{e^{-lambda}}{z}big(Ei(lambda t)-Ei(lambda t(z-1))big)|_0^1=frac{e^{-lambda}}{z}Big(ln(1-z)+Gamma(0,lambda(z-1))-Gamma(0,lambda)Big)$ what was seen by Claude Leibovici in advance. The approximation could be a nother exercise, I start to learn this topic. Best regards,
$endgroup$
– JV.Stalker
Jan 27 at 5:15
$begingroup$
@John, Sorry I leave out the "exponential" expression from my sentence. Accordace with Wolfram Alpha the last integral equal to: $frac{e^{-lambda}}{z}big(Ei(lambda t)-Ei(lambda t(z-1))big)|_0^1=frac{e^{-lambda}}{z}Big(ln(1-z)+Gamma(0,lambda(z-1))-Gamma(0,lambda)Big)$ what was seen by Claude Leibovici in advance. The approximation could be a nother exercise, I start to learn this topic. Best regards,
$endgroup$
– JV.Stalker
Jan 27 at 5:15
add a comment |
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