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d="scan'208,217";a="328328963" X-MGA-submission: =?us-ascii?q?MDHrpPc/yo52IcVDmDPAsy5fiJCW2vFVFXiMKm?= =?us-ascii?q?Zaf1skuL7S2S7dxaMDBm/Hv3Npx4/Yiof6xAKeecduXarXt8n+m0RXjN?= =?us-ascii?q?S66FO4IJ2qrl79dWaQVNI8wFQOl4tuAZ254o47iXTyrF8QI0SwqhriYD?= =?us-ascii?q?USUYHT3iTFpVXb2at2bbDywA=3D=3D?= Received: from relay11.mail.gandi.net ([217.70.178.231]) by mail3-smtp-sop.national.inria.fr with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 28 Nov 2019 10:30:14 +0100 Received: from sogo10.sd4.0x35.net (sogo10.sd4.0x35.net [10.200.201.60]) (Authenticated sender: basile@starynkevitch.net) by relay11.mail.gandi.net (Postfix) with ESMTPA id 9F20F10001B; Thu, 28 Nov 2019 09:30:10 +0000 (UTC) Content-Type: multipart/alternative; boundary="----=_=-_OpenGroupware_org_NGMime-8117-1574933410.309710-52------" In-Reply-To: <5cef-5ddf9300-35-4e2fd700@138599352> From: =?utf-8?q?basile=40starynkevitch=2Enet?= X-Forward: 127.0.0.1 Date: Thu, 28 Nov 2019 10:30:10 +0100 Cc: caml-list@inria.fr To: =?utf-8?q?Fran=C3=A7ois_Pottier?= MIME-Version: 1.0 Message-ID: <1fb5-5ddf9380-79-5558b880@243503475> User-Agent: SOGoMail 4.0.8 Subject: Re: [Caml-list] zarith: how to pick a random integer? ------=_=-_OpenGroupware_org_NGMime-8117-1574933410.309710-52------ Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Length: 1267 On Thursday, November 28, 2019 10:27 CET, basile@starynkevitch.net wrote: Sorry for the important typo. Corrected below On Wednesday, November 27, 2019 22:31 CET, Fran=C3=A7ois Pottier wrote: =C2=A0 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! =C2=A0 I tend to believe that the following idea might be good, but please check w= ith real probability experts. I definitely am not one (but one of my best c= olleagues 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 N would be that P But check with an expert, I am not one -- Basile Starynkevitch http://starynkevitch.net/Basile =C2=A0 =C2=A0 ------=_=-_OpenGroupware_org_NGMime-8117-1574933410.309710-52------ Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Length: 1665
On Thursday, November 28, 2019 10:27 CET, basile@starynkevitch.= net <basile@starynkevitch.net> wrote:


Sorry for the = important typo. Corrected below

On Wednesday, November 27, 2019 = 22:31 CET, Fran=C3=A7ois 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 lik= e a function
Z.random of type Z.t -> Z.t, but this function seems t= o be
missing, and I am not sure how to program it in an efficient
and correct way. Any suggestions would be welcome. Thanks!

&nbs= p;

I tend to believe that the following idea might be goo= d, 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 infini= tium


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 N would be tha= t P

But check with an expert, I am not one

--
Basile Starynkevitch http://starynkevitch.net/Basile
 
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