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```From: basile@starynkevitch.net <basile@starynkevitch.net>
To: François Pottier <francois.pottier@inria.fr>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] zarith: how to  pick a random integer?
Date: Thu, 28 Nov 2019 10:27:17 +0100
Message-ID: <5cef-5ddf9300-35-4e2fd700@138599352> (raw)

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On Wednesday, November 27, 2019 22:31 CET, François Pottier <francois.pottier@inria.fr> wrote:

Hello,

I am using zarith and would like to pick a random integer
comprised between 0 and some bound. I would like a function
Z.random of type Z.t -> Z.t, but this function seems to be
missing, and I am not sure how to program it in an efficient
and correct way. Any suggestions would be welcome. Thanks!

I tend to believe that the following idea might be good, but please check with real probability experts. I definitely am not one (but one of my best colleagues is one).

Let B be the bound.

You take a random number modulus 2*B. Let R be that number

You modelize the [0;B[ interval as a ring of numbers. For example if B is 5 : 0 -> 1 -> 2 -> 3 -> 4 -> 0 -> 1 -> .... ad infinitium

You memoize the previously given random number N

On that ring, you go R steps forward and obtain P. That is your new random number and on the next iteration the R would be that P

But check with an expert, I am not one

--

Basile

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```

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Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-27 21:31 François Pottier
2019-11-27 21:52 ` Carl Eastlund
2019-11-28  8:13   ` François Pottier
2019-11-28  9:27 basile [this message]
2019-11-28  9:30 ` basile
```

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