How to get the value of 'scaled' binomial distribution?












0












$begingroup$


People kindly told me that there is not a equivalent popular distribution for $aX$ when $X$ is distributed as Binomial, but it is just a 'scaled' distribution. Here, $a$ is a positive constant.



Question



How to get the value of 'scaled' binomial distribution? Do I need to use $Gamma$ function? A simpler way is appreciated.



To be more precise, I want to calculate $$g(x) = frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac xa} (1-p)^{(n-frac xa)},$$ where $f(x)$ is $B(n,p)$ and $a$ is positive constant.



What is the simplest way to calculate $g(x)$?



Background



I'm considering this question under the same condition with this question, where $X$ is distributed as $Binomial$ and I want to know the distribution of $aX$. $a$ is a real and positive number.



I know
$aX sim frac{1}{|a|}f(frac xa)$ ($f$ means the distribution of $X$),so I tried to calculate the probability of $aX$ by $frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac ax} (1-p)^{(n-frac xa)}$. But, this was not easy for me because $x/a$ is not a integer.



I think with $Gamma$ function $nCr$ can be calculated for any real number $r (< n)$. But is there any straightforward way to calculate 'scaled' binomial distribution?










share|cite|improve this question











$endgroup$












  • $begingroup$
    You may want to look at the beta function—en.wikipedia.org/wiki/Beta_function—as it provides a way to extend the binomial distribution to real values. (It's indicated near the end of the "Properties" section.)
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:54










  • $begingroup$
    So, yes, you will need to use the gamma function. I suspect there's no way around it for your application.
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:55










  • $begingroup$
    @BrianTung thank you. This is what I'm looking for. If you replace your comment to an answer, I would give a check mark :)
    $endgroup$
    – rkjt50r983
    Apr 28 '15 at 2:15












  • $begingroup$
    Thanks for your kind offer! But I'd probably only move it to an answer if you're looking to give out a checkmark. (I don't remember if you get any points for doing that.) Otherwise, if my contribution is merely a link to another page, I generally leave it in a comment. If it helped you out, that's good enough for me.
    $endgroup$
    – Brian Tung
    Apr 28 '15 at 16:23










  • $begingroup$
    @rkjt50r983, your scale function is not a density function because it does not normalise to 1. I think you consider that as a critical issue as well.
    $endgroup$
    – Chamberlain Foncha
    Nov 12 '17 at 15:01
















0












$begingroup$


People kindly told me that there is not a equivalent popular distribution for $aX$ when $X$ is distributed as Binomial, but it is just a 'scaled' distribution. Here, $a$ is a positive constant.



Question



How to get the value of 'scaled' binomial distribution? Do I need to use $Gamma$ function? A simpler way is appreciated.



To be more precise, I want to calculate $$g(x) = frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac xa} (1-p)^{(n-frac xa)},$$ where $f(x)$ is $B(n,p)$ and $a$ is positive constant.



What is the simplest way to calculate $g(x)$?



Background



I'm considering this question under the same condition with this question, where $X$ is distributed as $Binomial$ and I want to know the distribution of $aX$. $a$ is a real and positive number.



I know
$aX sim frac{1}{|a|}f(frac xa)$ ($f$ means the distribution of $X$),so I tried to calculate the probability of $aX$ by $frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac ax} (1-p)^{(n-frac xa)}$. But, this was not easy for me because $x/a$ is not a integer.



I think with $Gamma$ function $nCr$ can be calculated for any real number $r (< n)$. But is there any straightforward way to calculate 'scaled' binomial distribution?










share|cite|improve this question











$endgroup$












  • $begingroup$
    You may want to look at the beta function—en.wikipedia.org/wiki/Beta_function—as it provides a way to extend the binomial distribution to real values. (It's indicated near the end of the "Properties" section.)
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:54










  • $begingroup$
    So, yes, you will need to use the gamma function. I suspect there's no way around it for your application.
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:55










  • $begingroup$
    @BrianTung thank you. This is what I'm looking for. If you replace your comment to an answer, I would give a check mark :)
    $endgroup$
    – rkjt50r983
    Apr 28 '15 at 2:15












  • $begingroup$
    Thanks for your kind offer! But I'd probably only move it to an answer if you're looking to give out a checkmark. (I don't remember if you get any points for doing that.) Otherwise, if my contribution is merely a link to another page, I generally leave it in a comment. If it helped you out, that's good enough for me.
    $endgroup$
    – Brian Tung
    Apr 28 '15 at 16:23










  • $begingroup$
    @rkjt50r983, your scale function is not a density function because it does not normalise to 1. I think you consider that as a critical issue as well.
    $endgroup$
    – Chamberlain Foncha
    Nov 12 '17 at 15:01














0












0








0





$begingroup$


People kindly told me that there is not a equivalent popular distribution for $aX$ when $X$ is distributed as Binomial, but it is just a 'scaled' distribution. Here, $a$ is a positive constant.



Question



How to get the value of 'scaled' binomial distribution? Do I need to use $Gamma$ function? A simpler way is appreciated.



To be more precise, I want to calculate $$g(x) = frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac xa} (1-p)^{(n-frac xa)},$$ where $f(x)$ is $B(n,p)$ and $a$ is positive constant.



What is the simplest way to calculate $g(x)$?



Background



I'm considering this question under the same condition with this question, where $X$ is distributed as $Binomial$ and I want to know the distribution of $aX$. $a$ is a real and positive number.



I know
$aX sim frac{1}{|a|}f(frac xa)$ ($f$ means the distribution of $X$),so I tried to calculate the probability of $aX$ by $frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac ax} (1-p)^{(n-frac xa)}$. But, this was not easy for me because $x/a$ is not a integer.



I think with $Gamma$ function $nCr$ can be calculated for any real number $r (< n)$. But is there any straightforward way to calculate 'scaled' binomial distribution?










share|cite|improve this question











$endgroup$




People kindly told me that there is not a equivalent popular distribution for $aX$ when $X$ is distributed as Binomial, but it is just a 'scaled' distribution. Here, $a$ is a positive constant.



Question



How to get the value of 'scaled' binomial distribution? Do I need to use $Gamma$ function? A simpler way is appreciated.



To be more precise, I want to calculate $$g(x) = frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac xa} (1-p)^{(n-frac xa)},$$ where $f(x)$ is $B(n,p)$ and $a$ is positive constant.



What is the simplest way to calculate $g(x)$?



Background



I'm considering this question under the same condition with this question, where $X$ is distributed as $Binomial$ and I want to know the distribution of $aX$. $a$ is a real and positive number.



I know
$aX sim frac{1}{|a|}f(frac xa)$ ($f$ means the distribution of $X$),so I tried to calculate the probability of $aX$ by $frac{1}{|a|}f(frac xa) = {n choose x/a} p^{frac ax} (1-p)^{(n-frac xa)}$. But, this was not easy for me because $x/a$ is not a integer.



I think with $Gamma$ function $nCr$ can be calculated for any real number $r (< n)$. But is there any straightforward way to calculate 'scaled' binomial distribution?







probability probability-distributions






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Apr 13 '17 at 12:19









Community

1




1










asked Apr 27 '15 at 10:11









rkjt50r983rkjt50r983

259210




259210












  • $begingroup$
    You may want to look at the beta function—en.wikipedia.org/wiki/Beta_function—as it provides a way to extend the binomial distribution to real values. (It's indicated near the end of the "Properties" section.)
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:54










  • $begingroup$
    So, yes, you will need to use the gamma function. I suspect there's no way around it for your application.
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:55










  • $begingroup$
    @BrianTung thank you. This is what I'm looking for. If you replace your comment to an answer, I would give a check mark :)
    $endgroup$
    – rkjt50r983
    Apr 28 '15 at 2:15












  • $begingroup$
    Thanks for your kind offer! But I'd probably only move it to an answer if you're looking to give out a checkmark. (I don't remember if you get any points for doing that.) Otherwise, if my contribution is merely a link to another page, I generally leave it in a comment. If it helped you out, that's good enough for me.
    $endgroup$
    – Brian Tung
    Apr 28 '15 at 16:23










  • $begingroup$
    @rkjt50r983, your scale function is not a density function because it does not normalise to 1. I think you consider that as a critical issue as well.
    $endgroup$
    – Chamberlain Foncha
    Nov 12 '17 at 15:01


















  • $begingroup$
    You may want to look at the beta function—en.wikipedia.org/wiki/Beta_function—as it provides a way to extend the binomial distribution to real values. (It's indicated near the end of the "Properties" section.)
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:54










  • $begingroup$
    So, yes, you will need to use the gamma function. I suspect there's no way around it for your application.
    $endgroup$
    – Brian Tung
    Apr 27 '15 at 16:55










  • $begingroup$
    @BrianTung thank you. This is what I'm looking for. If you replace your comment to an answer, I would give a check mark :)
    $endgroup$
    – rkjt50r983
    Apr 28 '15 at 2:15












  • $begingroup$
    Thanks for your kind offer! But I'd probably only move it to an answer if you're looking to give out a checkmark. (I don't remember if you get any points for doing that.) Otherwise, if my contribution is merely a link to another page, I generally leave it in a comment. If it helped you out, that's good enough for me.
    $endgroup$
    – Brian Tung
    Apr 28 '15 at 16:23










  • $begingroup$
    @rkjt50r983, your scale function is not a density function because it does not normalise to 1. I think you consider that as a critical issue as well.
    $endgroup$
    – Chamberlain Foncha
    Nov 12 '17 at 15:01
















$begingroup$
You may want to look at the beta function—en.wikipedia.org/wiki/Beta_function—as it provides a way to extend the binomial distribution to real values. (It's indicated near the end of the "Properties" section.)
$endgroup$
– Brian Tung
Apr 27 '15 at 16:54




$begingroup$
You may want to look at the beta function—en.wikipedia.org/wiki/Beta_function—as it provides a way to extend the binomial distribution to real values. (It's indicated near the end of the "Properties" section.)
$endgroup$
– Brian Tung
Apr 27 '15 at 16:54












$begingroup$
So, yes, you will need to use the gamma function. I suspect there's no way around it for your application.
$endgroup$
– Brian Tung
Apr 27 '15 at 16:55




$begingroup$
So, yes, you will need to use the gamma function. I suspect there's no way around it for your application.
$endgroup$
– Brian Tung
Apr 27 '15 at 16:55












$begingroup$
@BrianTung thank you. This is what I'm looking for. If you replace your comment to an answer, I would give a check mark :)
$endgroup$
– rkjt50r983
Apr 28 '15 at 2:15






$begingroup$
@BrianTung thank you. This is what I'm looking for. If you replace your comment to an answer, I would give a check mark :)
$endgroup$
– rkjt50r983
Apr 28 '15 at 2:15














$begingroup$
Thanks for your kind offer! But I'd probably only move it to an answer if you're looking to give out a checkmark. (I don't remember if you get any points for doing that.) Otherwise, if my contribution is merely a link to another page, I generally leave it in a comment. If it helped you out, that's good enough for me.
$endgroup$
– Brian Tung
Apr 28 '15 at 16:23




$begingroup$
Thanks for your kind offer! But I'd probably only move it to an answer if you're looking to give out a checkmark. (I don't remember if you get any points for doing that.) Otherwise, if my contribution is merely a link to another page, I generally leave it in a comment. If it helped you out, that's good enough for me.
$endgroup$
– Brian Tung
Apr 28 '15 at 16:23












$begingroup$
@rkjt50r983, your scale function is not a density function because it does not normalise to 1. I think you consider that as a critical issue as well.
$endgroup$
– Chamberlain Foncha
Nov 12 '17 at 15:01




$begingroup$
@rkjt50r983, your scale function is not a density function because it does not normalise to 1. I think you consider that as a critical issue as well.
$endgroup$
– Chamberlain Foncha
Nov 12 '17 at 15:01










1 Answer
1






active

oldest

votes


















0












$begingroup$

For a random variable $X$ of binomial distribution of parameters $n,p$ the possible values taken are $0,1,2, cdots, n$ with probabilities$$P(X=k)={n choose k}p^k(1-p)^{n-k}.$$
If $a$ is a real constant and $Y=aX$ then the valueas taken by $Y$ are $1a,2a,cdots , na$ with probabilities $$P(Y=ak)=P(X=k).$$
I don't know if this answers the question.



EDITED



Perhaps, the reason of confusion is that there is no pdf. The cdf is
$$F_Y(x)=P(aX<x)=Pleft(X<frac{x}{a}right)=F_Xleft(frac{x}{a}right).$$



If the derivative existed then one could get a formula similar to what you quoted for the Gaussian distribution.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    thank you, but I think it is necessary to calculate ${n choose k/a}p^{k/a}(1-p)^{n-k/a}.$. More specifically, how do I define and calculate ${n choose k/a}$?
    $endgroup$
    – rkjt50r983
    Apr 27 '15 at 10:47












  • $begingroup$
    @rkjt50r938, The probabilities that $Y=ai$ are given. What else would want anybody know? The is no pdf in this case. Perhaps you want see the form of the cdf??
    $endgroup$
    – zoli
    Apr 27 '15 at 10:55










  • $begingroup$
    @rkjt50r938: I've edited my answer.
    $endgroup$
    – zoli
    Apr 27 '15 at 11:39











Your Answer





StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});














draft saved

draft discarded


















StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f1254069%2fhow-to-get-the-value-of-scaled-binomial-distribution%23new-answer', 'question_page');
}
);

Post as a guest















Required, but never shown

























1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









0












$begingroup$

For a random variable $X$ of binomial distribution of parameters $n,p$ the possible values taken are $0,1,2, cdots, n$ with probabilities$$P(X=k)={n choose k}p^k(1-p)^{n-k}.$$
If $a$ is a real constant and $Y=aX$ then the valueas taken by $Y$ are $1a,2a,cdots , na$ with probabilities $$P(Y=ak)=P(X=k).$$
I don't know if this answers the question.



EDITED



Perhaps, the reason of confusion is that there is no pdf. The cdf is
$$F_Y(x)=P(aX<x)=Pleft(X<frac{x}{a}right)=F_Xleft(frac{x}{a}right).$$



If the derivative existed then one could get a formula similar to what you quoted for the Gaussian distribution.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    thank you, but I think it is necessary to calculate ${n choose k/a}p^{k/a}(1-p)^{n-k/a}.$. More specifically, how do I define and calculate ${n choose k/a}$?
    $endgroup$
    – rkjt50r983
    Apr 27 '15 at 10:47












  • $begingroup$
    @rkjt50r938, The probabilities that $Y=ai$ are given. What else would want anybody know? The is no pdf in this case. Perhaps you want see the form of the cdf??
    $endgroup$
    – zoli
    Apr 27 '15 at 10:55










  • $begingroup$
    @rkjt50r938: I've edited my answer.
    $endgroup$
    – zoli
    Apr 27 '15 at 11:39
















0












$begingroup$

For a random variable $X$ of binomial distribution of parameters $n,p$ the possible values taken are $0,1,2, cdots, n$ with probabilities$$P(X=k)={n choose k}p^k(1-p)^{n-k}.$$
If $a$ is a real constant and $Y=aX$ then the valueas taken by $Y$ are $1a,2a,cdots , na$ with probabilities $$P(Y=ak)=P(X=k).$$
I don't know if this answers the question.



EDITED



Perhaps, the reason of confusion is that there is no pdf. The cdf is
$$F_Y(x)=P(aX<x)=Pleft(X<frac{x}{a}right)=F_Xleft(frac{x}{a}right).$$



If the derivative existed then one could get a formula similar to what you quoted for the Gaussian distribution.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    thank you, but I think it is necessary to calculate ${n choose k/a}p^{k/a}(1-p)^{n-k/a}.$. More specifically, how do I define and calculate ${n choose k/a}$?
    $endgroup$
    – rkjt50r983
    Apr 27 '15 at 10:47












  • $begingroup$
    @rkjt50r938, The probabilities that $Y=ai$ are given. What else would want anybody know? The is no pdf in this case. Perhaps you want see the form of the cdf??
    $endgroup$
    – zoli
    Apr 27 '15 at 10:55










  • $begingroup$
    @rkjt50r938: I've edited my answer.
    $endgroup$
    – zoli
    Apr 27 '15 at 11:39














0












0








0





$begingroup$

For a random variable $X$ of binomial distribution of parameters $n,p$ the possible values taken are $0,1,2, cdots, n$ with probabilities$$P(X=k)={n choose k}p^k(1-p)^{n-k}.$$
If $a$ is a real constant and $Y=aX$ then the valueas taken by $Y$ are $1a,2a,cdots , na$ with probabilities $$P(Y=ak)=P(X=k).$$
I don't know if this answers the question.



EDITED



Perhaps, the reason of confusion is that there is no pdf. The cdf is
$$F_Y(x)=P(aX<x)=Pleft(X<frac{x}{a}right)=F_Xleft(frac{x}{a}right).$$



If the derivative existed then one could get a formula similar to what you quoted for the Gaussian distribution.






share|cite|improve this answer











$endgroup$



For a random variable $X$ of binomial distribution of parameters $n,p$ the possible values taken are $0,1,2, cdots, n$ with probabilities$$P(X=k)={n choose k}p^k(1-p)^{n-k}.$$
If $a$ is a real constant and $Y=aX$ then the valueas taken by $Y$ are $1a,2a,cdots , na$ with probabilities $$P(Y=ak)=P(X=k).$$
I don't know if this answers the question.



EDITED



Perhaps, the reason of confusion is that there is no pdf. The cdf is
$$F_Y(x)=P(aX<x)=Pleft(X<frac{x}{a}right)=F_Xleft(frac{x}{a}right).$$



If the derivative existed then one could get a formula similar to what you quoted for the Gaussian distribution.







share|cite|improve this answer














share|cite|improve this answer



share|cite|improve this answer








edited Apr 27 '15 at 18:16

























answered Apr 27 '15 at 10:35









zolizoli

17k41945




17k41945












  • $begingroup$
    thank you, but I think it is necessary to calculate ${n choose k/a}p^{k/a}(1-p)^{n-k/a}.$. More specifically, how do I define and calculate ${n choose k/a}$?
    $endgroup$
    – rkjt50r983
    Apr 27 '15 at 10:47












  • $begingroup$
    @rkjt50r938, The probabilities that $Y=ai$ are given. What else would want anybody know? The is no pdf in this case. Perhaps you want see the form of the cdf??
    $endgroup$
    – zoli
    Apr 27 '15 at 10:55










  • $begingroup$
    @rkjt50r938: I've edited my answer.
    $endgroup$
    – zoli
    Apr 27 '15 at 11:39


















  • $begingroup$
    thank you, but I think it is necessary to calculate ${n choose k/a}p^{k/a}(1-p)^{n-k/a}.$. More specifically, how do I define and calculate ${n choose k/a}$?
    $endgroup$
    – rkjt50r983
    Apr 27 '15 at 10:47












  • $begingroup$
    @rkjt50r938, The probabilities that $Y=ai$ are given. What else would want anybody know? The is no pdf in this case. Perhaps you want see the form of the cdf??
    $endgroup$
    – zoli
    Apr 27 '15 at 10:55










  • $begingroup$
    @rkjt50r938: I've edited my answer.
    $endgroup$
    – zoli
    Apr 27 '15 at 11:39
















$begingroup$
thank you, but I think it is necessary to calculate ${n choose k/a}p^{k/a}(1-p)^{n-k/a}.$. More specifically, how do I define and calculate ${n choose k/a}$?
$endgroup$
– rkjt50r983
Apr 27 '15 at 10:47






$begingroup$
thank you, but I think it is necessary to calculate ${n choose k/a}p^{k/a}(1-p)^{n-k/a}.$. More specifically, how do I define and calculate ${n choose k/a}$?
$endgroup$
– rkjt50r983
Apr 27 '15 at 10:47














$begingroup$
@rkjt50r938, The probabilities that $Y=ai$ are given. What else would want anybody know? The is no pdf in this case. Perhaps you want see the form of the cdf??
$endgroup$
– zoli
Apr 27 '15 at 10:55




$begingroup$
@rkjt50r938, The probabilities that $Y=ai$ are given. What else would want anybody know? The is no pdf in this case. Perhaps you want see the form of the cdf??
$endgroup$
– zoli
Apr 27 '15 at 10:55












$begingroup$
@rkjt50r938: I've edited my answer.
$endgroup$
– zoli
Apr 27 '15 at 11:39




$begingroup$
@rkjt50r938: I've edited my answer.
$endgroup$
– zoli
Apr 27 '15 at 11:39


















draft saved

draft discarded




















































Thanks for contributing an answer to Mathematics Stack Exchange!


  • Please be sure to answer the question. Provide details and share your research!

But avoid



  • Asking for help, clarification, or responding to other answers.

  • Making statements based on opinion; back them up with references or personal experience.


Use MathJax to format equations. MathJax reference.


To learn more, see our tips on writing great answers.




draft saved


draft discarded














StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f1254069%2fhow-to-get-the-value-of-scaled-binomial-distribution%23new-answer', 'question_page');
}
);

Post as a guest















Required, but never shown





















































Required, but never shown














Required, but never shown












Required, but never shown







Required, but never shown

































Required, but never shown














Required, but never shown












Required, but never shown







Required, but never shown







Popular posts from this blog

Can a sorcerer learn a 5th-level spell early by creating spell slots using the Font of Magic feature?

ts Property 'filter' does not exist on type '{}'

Notepad++ export/extract a list of installed plugins