# Random algorithm

Dave Cragg dave.cragg at lacscentre.co.uk
Thu Nov 13 03:27:13 CST 2008

```But I think the principal behind generating random numbers is
different from generating a random seed. If we could generate a
reliably random randomSeed then we would never need to do it.  We
would be just as well to generate a reliably random sequence of random
numbers.

On 13 Nov 2008, at 02:18, Randall Reetz wrote:

> There is a huge difference between random and unique.  If you are
> after unique then just use the counting numbers.  If you need both
> random and unique you will have to check each number generated
> against a saved list of every previous number.  There is nothing
> wrong with a random number generator that spits out duplicate
> numbers.  Random is blind to history (and future).  Random is not
> nostalgic.  A coin with two sides is just as good at random as a
> pair of thousand sided dice.
>
> Randall
>
> -----Original Message-----
> From: "Dave Cragg" <dave.cragg at lacscentre.co.uk>
> To: "How to use Revolution" <use-revolution at lists.runrev.com>
> Sent: 11/12/2008 5:26 PM
> Subject: Re: Random algorithm
>
>> It would seem that resetting the randomSeed each time you use the
>> random function would only have a 1-in-4,570,422 chance of getting
>> the same seed as the previous run, no?
>
> Yes, but the chances of having the same seed as any of teh previous
> runs becomes progressively larger. Is it not a bit like the shared
> birthdays in a classroom. It only takes 23 people gathered in a room
> to make the chance of two of them sharing a birthday more than 50%.
>
> From my probably poor calculation, I think if you ran your randomSeed
> algorithm about 2500 times, there would be a 50% chance that the same
> randomSeed had been chosen at least twice. (At 4000, I think the
> chance is over 80%) In many situations, I think a repeated sequence
> would be worse than a biased sequence.
>
> A long time since I did this kind of thing, so apologies if I have
> this wrong.
>
> Dave
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```

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