Re: [R] Sum(Random Numbers)=100

From: Moshe Olshansky <m_olshansky_at_yahoo.com>
Date: Mon, 07 Jul 2008 23:39:05 -0700 (PDT)


If they are really random you can not expect their sum to be 100. However, it is not difficult to get that given that the sum of n independent Poisson random variables equals N, any individual one has the conditional binomial distribution with size = N and p = 1/n, i.e. P(Xi=k/Sn=N) = (N over k)*(1/n)^k*((n-1)/n)^(N-k). So you can generate X1 binomial with size = 100 and p = 1/50; if X1 = k1 then the sum of the rest 49 must equal 100 - k1, so now you generate X2 binomial with size = 100-k1 and p = 1/49; if X2 = k2 then generate X3 binomial with size = 100 -(k1+k2) and p = 1/48, etc.

Why do you need this?

> From: Shubha Vishwanath Karanth <shubhak_at_ambaresearch.com>
> Subject: [R] Sum(Random Numbers)=100
> To: r-help@stat.math.ethz.ch
> Received: Tuesday, 8 July, 2008, 3:58 PM
> Hi R,
>
>
>
> I need to generate 50 random numbers (preferably poisson),
> such that
> their sum is equal to 100. How do I do this?
>
>
>
>
>
> Thank you,
>
> Shubha
>
>
>
> This e-mail may contain confidential and/or privileged
> i...{{dropped:13}}
>
> ______________________________________________
> R-help_at_r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained,
> reproducible code.



R-help_at_r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 08 Jul 2008 - 06:43:30 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Tue 08 Jul 2008 - 07:31:48 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.

list of date sections of archive