What is the asymptotic order of $sum_{k=0}^n {nchoose k}^2$?
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What is the asymptotic order of $sum_{k=0}^n {nchoose k}^2$? That is, find $g(n)$ such that $$lim_{nto infty}frac{sum_{k=0}^n {nchoose k}^2}{g(n)}=1$$
We can expand the binomial coefficient and use Stirling's approximation but I can not determine g(n).
probability asymptotics
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add a comment |
$begingroup$
What is the asymptotic order of $sum_{k=0}^n {nchoose k}^2$? That is, find $g(n)$ such that $$lim_{nto infty}frac{sum_{k=0}^n {nchoose k}^2}{g(n)}=1$$
We can expand the binomial coefficient and use Stirling's approximation but I can not determine g(n).
probability asymptotics
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6
$begingroup$
Were you able to simplify the summation to $binom{2n}{n}$?
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– JimmyK4542
Dec 5 '18 at 2:27
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From here: math.stackexchange.com/questions/3025663/… you should now be able to solve it much easier
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– Henry Lee
Dec 5 '18 at 2:28
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I see, thank you. So $g(n)=frac{4^n}{sqrt{pi n}}$
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– Probability student
Dec 5 '18 at 2:37
1
$begingroup$
What do we get if we have $sum_{k=0}^n{n choose k}{n+1 choose k}$?
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– Probability student
Dec 5 '18 at 2:44
$begingroup$
See here math.stackexchange.com/questions/74651/…
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– leonbloy
Dec 5 '18 at 3:27
add a comment |
$begingroup$
What is the asymptotic order of $sum_{k=0}^n {nchoose k}^2$? That is, find $g(n)$ such that $$lim_{nto infty}frac{sum_{k=0}^n {nchoose k}^2}{g(n)}=1$$
We can expand the binomial coefficient and use Stirling's approximation but I can not determine g(n).
probability asymptotics
$endgroup$
What is the asymptotic order of $sum_{k=0}^n {nchoose k}^2$? That is, find $g(n)$ such that $$lim_{nto infty}frac{sum_{k=0}^n {nchoose k}^2}{g(n)}=1$$
We can expand the binomial coefficient and use Stirling's approximation but I can not determine g(n).
probability asymptotics
probability asymptotics
asked Dec 5 '18 at 2:17
Probability studentProbability student
213
213
6
$begingroup$
Were you able to simplify the summation to $binom{2n}{n}$?
$endgroup$
– JimmyK4542
Dec 5 '18 at 2:27
$begingroup$
From here: math.stackexchange.com/questions/3025663/… you should now be able to solve it much easier
$endgroup$
– Henry Lee
Dec 5 '18 at 2:28
$begingroup$
I see, thank you. So $g(n)=frac{4^n}{sqrt{pi n}}$
$endgroup$
– Probability student
Dec 5 '18 at 2:37
1
$begingroup$
What do we get if we have $sum_{k=0}^n{n choose k}{n+1 choose k}$?
$endgroup$
– Probability student
Dec 5 '18 at 2:44
$begingroup$
See here math.stackexchange.com/questions/74651/…
$endgroup$
– leonbloy
Dec 5 '18 at 3:27
add a comment |
6
$begingroup$
Were you able to simplify the summation to $binom{2n}{n}$?
$endgroup$
– JimmyK4542
Dec 5 '18 at 2:27
$begingroup$
From here: math.stackexchange.com/questions/3025663/… you should now be able to solve it much easier
$endgroup$
– Henry Lee
Dec 5 '18 at 2:28
$begingroup$
I see, thank you. So $g(n)=frac{4^n}{sqrt{pi n}}$
$endgroup$
– Probability student
Dec 5 '18 at 2:37
1
$begingroup$
What do we get if we have $sum_{k=0}^n{n choose k}{n+1 choose k}$?
$endgroup$
– Probability student
Dec 5 '18 at 2:44
$begingroup$
See here math.stackexchange.com/questions/74651/…
$endgroup$
– leonbloy
Dec 5 '18 at 3:27
6
6
$begingroup$
Were you able to simplify the summation to $binom{2n}{n}$?
$endgroup$
– JimmyK4542
Dec 5 '18 at 2:27
$begingroup$
Were you able to simplify the summation to $binom{2n}{n}$?
$endgroup$
– JimmyK4542
Dec 5 '18 at 2:27
$begingroup$
From here: math.stackexchange.com/questions/3025663/… you should now be able to solve it much easier
$endgroup$
– Henry Lee
Dec 5 '18 at 2:28
$begingroup$
From here: math.stackexchange.com/questions/3025663/… you should now be able to solve it much easier
$endgroup$
– Henry Lee
Dec 5 '18 at 2:28
$begingroup$
I see, thank you. So $g(n)=frac{4^n}{sqrt{pi n}}$
$endgroup$
– Probability student
Dec 5 '18 at 2:37
$begingroup$
I see, thank you. So $g(n)=frac{4^n}{sqrt{pi n}}$
$endgroup$
– Probability student
Dec 5 '18 at 2:37
1
1
$begingroup$
What do we get if we have $sum_{k=0}^n{n choose k}{n+1 choose k}$?
$endgroup$
– Probability student
Dec 5 '18 at 2:44
$begingroup$
What do we get if we have $sum_{k=0}^n{n choose k}{n+1 choose k}$?
$endgroup$
– Probability student
Dec 5 '18 at 2:44
$begingroup$
See here math.stackexchange.com/questions/74651/…
$endgroup$
– leonbloy
Dec 5 '18 at 3:27
$begingroup$
See here math.stackexchange.com/questions/74651/…
$endgroup$
– leonbloy
Dec 5 '18 at 3:27
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = sum_{k=0}^n binom{n}{n-k}binom{n+m}{k}.$$
This counts the number of ways to choose $n$ objects from a set of $n+2m$. To see this, let there be $n$ red ones and $n+m$ blue ones, and do casework on how many red and how many blue we choose. So:
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = binom{2n+m}{n}.$$
I think, using Stirling's formula, you can probably do the rest.
$endgroup$
$begingroup$
Thanks Carl. I think it should be $${2n+m choose n}$$
$endgroup$
– Probability student
Dec 5 '18 at 3:19
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@Probabilitystudent Thanks -- I've fixed it.
$endgroup$
– Carl Schildkraut
Dec 5 '18 at 3:47
add a comment |
$begingroup$
This is a comment regarding
the comment of Probability student:
According to Wolfy,
$sum_{k=0}^n({n choose k}{n+1choose k})
= dfrac{2^{2n+1}(n + 1/2)!}{sqrt{π} (n + 1)!}
$
$sum_{k=0}^n({n choose k}{n+2choose k})
= dfrac{2^{2n + 2} (n + 1) (n + 1/2)!}{sqrt{π} (n + 2)!}
$
Looks like it might be possible
to get a closed form for
$sum_{k=0}^n({n choose k}{n+mchoose k})$.
And Wolfy says that
$sum_{k=0}^n({n choose k}{n+mchoose k})
=dfrac{(m + 2 n)!}{n! (m + n)!}
$.
$endgroup$
1
$begingroup$
thank you but what is Wolfy? How do you get the first result, for instance? Thanks!
$endgroup$
– Probability student
Dec 5 '18 at 3:04
$begingroup$
"Wolfy" is my pet term for Wolfram Alpha. I often throw expressions at it to see what happens.
$endgroup$
– marty cohen
Dec 5 '18 at 3:09
add a comment |
$begingroup$
If you use marty cohen's answer, taking the logarithm and then using Stirling approximation, you should get something like
$$log left(frac{(m+2 n)!}{n! (m+n)!}right)=2 n log (2)+log left(frac{2^m}{sqrt{pi n}}right)-frac{2 m^2+2 m+1}{8
n}+Oleft(frac{1}{n^2}right)$$ and then, for large values of $n$,
$$frac{(m+2 n)!}{n! (m+n)!} sim frac{2^{2n+m}} {sqrt{pi n}}$$ What is interesting (at least to me) is the next term which shows how is approached the asymptotics.
$endgroup$
$begingroup$
Thanks! I think it should be $$sim frac{2^{2n+m}e^{m}}{sqrt{pi n}}$$
$endgroup$
– Probability student
Dec 5 '18 at 10:24
add a comment |
Your Answer
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3 Answers
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3 Answers
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$begingroup$
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = sum_{k=0}^n binom{n}{n-k}binom{n+m}{k}.$$
This counts the number of ways to choose $n$ objects from a set of $n+2m$. To see this, let there be $n$ red ones and $n+m$ blue ones, and do casework on how many red and how many blue we choose. So:
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = binom{2n+m}{n}.$$
I think, using Stirling's formula, you can probably do the rest.
$endgroup$
$begingroup$
Thanks Carl. I think it should be $${2n+m choose n}$$
$endgroup$
– Probability student
Dec 5 '18 at 3:19
$begingroup$
@Probabilitystudent Thanks -- I've fixed it.
$endgroup$
– Carl Schildkraut
Dec 5 '18 at 3:47
add a comment |
$begingroup$
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = sum_{k=0}^n binom{n}{n-k}binom{n+m}{k}.$$
This counts the number of ways to choose $n$ objects from a set of $n+2m$. To see this, let there be $n$ red ones and $n+m$ blue ones, and do casework on how many red and how many blue we choose. So:
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = binom{2n+m}{n}.$$
I think, using Stirling's formula, you can probably do the rest.
$endgroup$
$begingroup$
Thanks Carl. I think it should be $${2n+m choose n}$$
$endgroup$
– Probability student
Dec 5 '18 at 3:19
$begingroup$
@Probabilitystudent Thanks -- I've fixed it.
$endgroup$
– Carl Schildkraut
Dec 5 '18 at 3:47
add a comment |
$begingroup$
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = sum_{k=0}^n binom{n}{n-k}binom{n+m}{k}.$$
This counts the number of ways to choose $n$ objects from a set of $n+2m$. To see this, let there be $n$ red ones and $n+m$ blue ones, and do casework on how many red and how many blue we choose. So:
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = binom{2n+m}{n}.$$
I think, using Stirling's formula, you can probably do the rest.
$endgroup$
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = sum_{k=0}^n binom{n}{n-k}binom{n+m}{k}.$$
This counts the number of ways to choose $n$ objects from a set of $n+2m$. To see this, let there be $n$ red ones and $n+m$ blue ones, and do casework on how many red and how many blue we choose. So:
$$sum_{k=0}^n binom{n}{k}binom{n+m}{k} = binom{2n+m}{n}.$$
I think, using Stirling's formula, you can probably do the rest.
edited Dec 5 '18 at 3:47
answered Dec 5 '18 at 3:14
Carl SchildkrautCarl Schildkraut
11.3k11441
11.3k11441
$begingroup$
Thanks Carl. I think it should be $${2n+m choose n}$$
$endgroup$
– Probability student
Dec 5 '18 at 3:19
$begingroup$
@Probabilitystudent Thanks -- I've fixed it.
$endgroup$
– Carl Schildkraut
Dec 5 '18 at 3:47
add a comment |
$begingroup$
Thanks Carl. I think it should be $${2n+m choose n}$$
$endgroup$
– Probability student
Dec 5 '18 at 3:19
$begingroup$
@Probabilitystudent Thanks -- I've fixed it.
$endgroup$
– Carl Schildkraut
Dec 5 '18 at 3:47
$begingroup$
Thanks Carl. I think it should be $${2n+m choose n}$$
$endgroup$
– Probability student
Dec 5 '18 at 3:19
$begingroup$
Thanks Carl. I think it should be $${2n+m choose n}$$
$endgroup$
– Probability student
Dec 5 '18 at 3:19
$begingroup$
@Probabilitystudent Thanks -- I've fixed it.
$endgroup$
– Carl Schildkraut
Dec 5 '18 at 3:47
$begingroup$
@Probabilitystudent Thanks -- I've fixed it.
$endgroup$
– Carl Schildkraut
Dec 5 '18 at 3:47
add a comment |
$begingroup$
This is a comment regarding
the comment of Probability student:
According to Wolfy,
$sum_{k=0}^n({n choose k}{n+1choose k})
= dfrac{2^{2n+1}(n + 1/2)!}{sqrt{π} (n + 1)!}
$
$sum_{k=0}^n({n choose k}{n+2choose k})
= dfrac{2^{2n + 2} (n + 1) (n + 1/2)!}{sqrt{π} (n + 2)!}
$
Looks like it might be possible
to get a closed form for
$sum_{k=0}^n({n choose k}{n+mchoose k})$.
And Wolfy says that
$sum_{k=0}^n({n choose k}{n+mchoose k})
=dfrac{(m + 2 n)!}{n! (m + n)!}
$.
$endgroup$
1
$begingroup$
thank you but what is Wolfy? How do you get the first result, for instance? Thanks!
$endgroup$
– Probability student
Dec 5 '18 at 3:04
$begingroup$
"Wolfy" is my pet term for Wolfram Alpha. I often throw expressions at it to see what happens.
$endgroup$
– marty cohen
Dec 5 '18 at 3:09
add a comment |
$begingroup$
This is a comment regarding
the comment of Probability student:
According to Wolfy,
$sum_{k=0}^n({n choose k}{n+1choose k})
= dfrac{2^{2n+1}(n + 1/2)!}{sqrt{π} (n + 1)!}
$
$sum_{k=0}^n({n choose k}{n+2choose k})
= dfrac{2^{2n + 2} (n + 1) (n + 1/2)!}{sqrt{π} (n + 2)!}
$
Looks like it might be possible
to get a closed form for
$sum_{k=0}^n({n choose k}{n+mchoose k})$.
And Wolfy says that
$sum_{k=0}^n({n choose k}{n+mchoose k})
=dfrac{(m + 2 n)!}{n! (m + n)!}
$.
$endgroup$
1
$begingroup$
thank you but what is Wolfy? How do you get the first result, for instance? Thanks!
$endgroup$
– Probability student
Dec 5 '18 at 3:04
$begingroup$
"Wolfy" is my pet term for Wolfram Alpha. I often throw expressions at it to see what happens.
$endgroup$
– marty cohen
Dec 5 '18 at 3:09
add a comment |
$begingroup$
This is a comment regarding
the comment of Probability student:
According to Wolfy,
$sum_{k=0}^n({n choose k}{n+1choose k})
= dfrac{2^{2n+1}(n + 1/2)!}{sqrt{π} (n + 1)!}
$
$sum_{k=0}^n({n choose k}{n+2choose k})
= dfrac{2^{2n + 2} (n + 1) (n + 1/2)!}{sqrt{π} (n + 2)!}
$
Looks like it might be possible
to get a closed form for
$sum_{k=0}^n({n choose k}{n+mchoose k})$.
And Wolfy says that
$sum_{k=0}^n({n choose k}{n+mchoose k})
=dfrac{(m + 2 n)!}{n! (m + n)!}
$.
$endgroup$
This is a comment regarding
the comment of Probability student:
According to Wolfy,
$sum_{k=0}^n({n choose k}{n+1choose k})
= dfrac{2^{2n+1}(n + 1/2)!}{sqrt{π} (n + 1)!}
$
$sum_{k=0}^n({n choose k}{n+2choose k})
= dfrac{2^{2n + 2} (n + 1) (n + 1/2)!}{sqrt{π} (n + 2)!}
$
Looks like it might be possible
to get a closed form for
$sum_{k=0}^n({n choose k}{n+mchoose k})$.
And Wolfy says that
$sum_{k=0}^n({n choose k}{n+mchoose k})
=dfrac{(m + 2 n)!}{n! (m + n)!}
$.
answered Dec 5 '18 at 3:00
marty cohenmarty cohen
73.3k549128
73.3k549128
1
$begingroup$
thank you but what is Wolfy? How do you get the first result, for instance? Thanks!
$endgroup$
– Probability student
Dec 5 '18 at 3:04
$begingroup$
"Wolfy" is my pet term for Wolfram Alpha. I often throw expressions at it to see what happens.
$endgroup$
– marty cohen
Dec 5 '18 at 3:09
add a comment |
1
$begingroup$
thank you but what is Wolfy? How do you get the first result, for instance? Thanks!
$endgroup$
– Probability student
Dec 5 '18 at 3:04
$begingroup$
"Wolfy" is my pet term for Wolfram Alpha. I often throw expressions at it to see what happens.
$endgroup$
– marty cohen
Dec 5 '18 at 3:09
1
1
$begingroup$
thank you but what is Wolfy? How do you get the first result, for instance? Thanks!
$endgroup$
– Probability student
Dec 5 '18 at 3:04
$begingroup$
thank you but what is Wolfy? How do you get the first result, for instance? Thanks!
$endgroup$
– Probability student
Dec 5 '18 at 3:04
$begingroup$
"Wolfy" is my pet term for Wolfram Alpha. I often throw expressions at it to see what happens.
$endgroup$
– marty cohen
Dec 5 '18 at 3:09
$begingroup$
"Wolfy" is my pet term for Wolfram Alpha. I often throw expressions at it to see what happens.
$endgroup$
– marty cohen
Dec 5 '18 at 3:09
add a comment |
$begingroup$
If you use marty cohen's answer, taking the logarithm and then using Stirling approximation, you should get something like
$$log left(frac{(m+2 n)!}{n! (m+n)!}right)=2 n log (2)+log left(frac{2^m}{sqrt{pi n}}right)-frac{2 m^2+2 m+1}{8
n}+Oleft(frac{1}{n^2}right)$$ and then, for large values of $n$,
$$frac{(m+2 n)!}{n! (m+n)!} sim frac{2^{2n+m}} {sqrt{pi n}}$$ What is interesting (at least to me) is the next term which shows how is approached the asymptotics.
$endgroup$
$begingroup$
Thanks! I think it should be $$sim frac{2^{2n+m}e^{m}}{sqrt{pi n}}$$
$endgroup$
– Probability student
Dec 5 '18 at 10:24
add a comment |
$begingroup$
If you use marty cohen's answer, taking the logarithm and then using Stirling approximation, you should get something like
$$log left(frac{(m+2 n)!}{n! (m+n)!}right)=2 n log (2)+log left(frac{2^m}{sqrt{pi n}}right)-frac{2 m^2+2 m+1}{8
n}+Oleft(frac{1}{n^2}right)$$ and then, for large values of $n$,
$$frac{(m+2 n)!}{n! (m+n)!} sim frac{2^{2n+m}} {sqrt{pi n}}$$ What is interesting (at least to me) is the next term which shows how is approached the asymptotics.
$endgroup$
$begingroup$
Thanks! I think it should be $$sim frac{2^{2n+m}e^{m}}{sqrt{pi n}}$$
$endgroup$
– Probability student
Dec 5 '18 at 10:24
add a comment |
$begingroup$
If you use marty cohen's answer, taking the logarithm and then using Stirling approximation, you should get something like
$$log left(frac{(m+2 n)!}{n! (m+n)!}right)=2 n log (2)+log left(frac{2^m}{sqrt{pi n}}right)-frac{2 m^2+2 m+1}{8
n}+Oleft(frac{1}{n^2}right)$$ and then, for large values of $n$,
$$frac{(m+2 n)!}{n! (m+n)!} sim frac{2^{2n+m}} {sqrt{pi n}}$$ What is interesting (at least to me) is the next term which shows how is approached the asymptotics.
$endgroup$
If you use marty cohen's answer, taking the logarithm and then using Stirling approximation, you should get something like
$$log left(frac{(m+2 n)!}{n! (m+n)!}right)=2 n log (2)+log left(frac{2^m}{sqrt{pi n}}right)-frac{2 m^2+2 m+1}{8
n}+Oleft(frac{1}{n^2}right)$$ and then, for large values of $n$,
$$frac{(m+2 n)!}{n! (m+n)!} sim frac{2^{2n+m}} {sqrt{pi n}}$$ What is interesting (at least to me) is the next term which shows how is approached the asymptotics.
answered Dec 5 '18 at 4:20
Claude LeiboviciClaude Leibovici
120k1157132
120k1157132
$begingroup$
Thanks! I think it should be $$sim frac{2^{2n+m}e^{m}}{sqrt{pi n}}$$
$endgroup$
– Probability student
Dec 5 '18 at 10:24
add a comment |
$begingroup$
Thanks! I think it should be $$sim frac{2^{2n+m}e^{m}}{sqrt{pi n}}$$
$endgroup$
– Probability student
Dec 5 '18 at 10:24
$begingroup$
Thanks! I think it should be $$sim frac{2^{2n+m}e^{m}}{sqrt{pi n}}$$
$endgroup$
– Probability student
Dec 5 '18 at 10:24
$begingroup$
Thanks! I think it should be $$sim frac{2^{2n+m}e^{m}}{sqrt{pi n}}$$
$endgroup$
– Probability student
Dec 5 '18 at 10:24
add a comment |
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Were you able to simplify the summation to $binom{2n}{n}$?
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– JimmyK4542
Dec 5 '18 at 2:27
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From here: math.stackexchange.com/questions/3025663/… you should now be able to solve it much easier
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– Henry Lee
Dec 5 '18 at 2:28
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I see, thank you. So $g(n)=frac{4^n}{sqrt{pi n}}$
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– Probability student
Dec 5 '18 at 2:37
1
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What do we get if we have $sum_{k=0}^n{n choose k}{n+1 choose k}$?
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– Probability student
Dec 5 '18 at 2:44
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See here math.stackexchange.com/questions/74651/…
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– leonbloy
Dec 5 '18 at 3:27