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MathGroup Archive 2004

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Re: populate a list with random numbers from normaldistribution?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49934] Re: populate a list with random numbers from normaldistribution?
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Fri, 6 Aug 2004 03:10:01 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 8/5/04 at 9:22 AM, sean_incali at yahoo.com (sean kim) wrote:

>What I wanted to do is to pick sets of random Integers in the
>ranges {10000, 99999} from the Normal distribution such that, the
>mean is 50000 and the standard deviation is 25000.

>or is that not normal distribution? will that be a custom
>distribution?

Exactly. A normal distribution is a continous distribution. A distribution defined over just integers by definition would be discrete and cannot be normal. Further, normal deviates range over +/- infinity not over 10000 to 99999

You could do something like

Table[Floor[Random[NormalDistribution[50000, 25000]]], {100}]

or 

Table[Round[Random[NormalDistribution[50000, 25000]]], {100}]

then discard any value less than 10000 or greater than 99999

Note neither of these will be normal but may well be close enough to normal for your purposes.

>if that isn't possible, then I want to pick set of random intgers
>ranging from {10000, 99999} such that the variance and the mean and
>standard deviation do not change across different runs.

That requirement is filled by Table[Random[Integer,{10000,99999}], {100}]

That is, as long as you are using a distribution that has a defined mean and variance and do not change the distribution parameters you the variance and mean will be consistent from run to run. If you need to guarantee exactly the same variance and mean, you will need to use SeedRandom with a specific value. This will give exactly the same set of numbers every run guaranteeing no change whatever in the variance and mean. Anything else mean some variation in statistical parameters.
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