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From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: draw normal random numbers with fixed sum
Date: Wed, 9 Mar 2011 04:19:26 -0800 (PST)
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On 9 Mrz., 12:46, "Claudia " <claudiahasens...@web.de> wrote:
> "John D'Errico" <woodch...@rochester.rr.com> wrote in message <il7nk2$g6...@fred.mathworks.com>...
> > "Claudia" wrote in message <il7mnh$j2...@fred.mathworks.com>...
> > > Hi all,
>
> > > I would like to draw a given number k of random numbers from a normal
> > > distribution with given parameters mu and sigma, and I would like the sum of this random numbers to be like another given parameter call it s.
>
> > > How can I do that in Matlab?
>
> > > Thank you in advance
>
> > If the sum is fixed, then they are not normally distributed,
> > unless the desired value of s is EXACTLY k*mu.
>
> > And even then, the numbers will not be normally distributed,
> > since you can only specify the mean of the POPULATION, not
> > of any sample from that distribution.
>
> > John
>
> Hi John,
>
> thanks for your answer!
>
> the value s is k*mu. okay, I explain my whole task:
>
> I have a normal distribution of produced Chips, from which I know the parameters mu and sigma.
> This distribution is the average of k independent normally distributed random variables with different parameters mu and the same parameter sigma.
> So, I think the mu's are also normally distributed with the given parameters of the Chip-distribution (mu and sigma).
> What I need are the mu's to calculate other things...
> But how can I generate them???- Zitierten Text ausblenden -
>
> - Zitierten Text anzeigen -

The mu_i 's are given and don't follow a distribution.
I don't know if it helps, but if
X = 1/k * sum_{i=1}^{k} X_i
and the X_i are normal random variables with expectation mu_i and
variance sigma^2,
then X also follows a normal distribution with mean mu = 1/k*sum_{i=1}
^{k} mu_i and
variance 1/k * sigma^2.

Best wishes
Torsten.