From ripley at stats.ox.ac.uk  Fri Nov  2 16:39:29 2012
From: ripley at stats.ox.ac.uk (Prof Brian Ripley)
Date: Fri, 2 Nov 2012 15:39:29 +0000 (GMT)
Subject: [Rd] An idea: Extend mclapply's mc.set.seed with an initial
 seed value?
In-Reply-To: <5093E24A.1030700@gmail.com>
References: <CAK7-yAiAfdBZQVbh2iqRknV9Q6Sjt1HRk4cgNRMgCbbDWeqCCw@mail.gmail.com>
	<5093E24A.1030700@gmail.com>
Message-ID: <alpine.LFD.2.02.1211021533130.10164@toucan.stats.ox.ac.uk>

On Fri, 2 Nov 2012, Paul Gilbert wrote:

> I appreciate your problem, and getting reproducible random generator results 
> on a parallel system is something to be careful about. However, I would avoid 
> making it too easy to have a fixed seed. In earlier days there were mistakes 
> too often made by users inadvertently using the same seed over and over again 
> (on simple single processor systems), for example, by reloading a session 
> with the seed set.

But R already makes what I take to be the wish really easy:

set.seed(123)
mclapply(...)

sets the same seed on each child.

And the other option, mc.set.seed = TRUE, makes it easy to have 
reproducibly different seeds on each child.  See 
?parallel::mcparallel .

>
> Paul
>
> On 12-11-01 08:46 PM, Ivan Popivanov wrote:
>> Hello,
>> 
>> Have been thinking that sometimes users may want each process to initialize
>> its random seed with a specific value rather then the current seed. This
>> could be keyed off depending whether mc.set.seed is logical, preserving the
>> current behaviour, or numerical, using the value in a call to set.seed.
>> Does this make sense?
>> 
>> If you wonder how I came up with the idea: I spent a couple of hours
>> debugging "unstable" results from parallel tuning of svms, which was caused
>> by the parallel execution. In my case I can simply do the set.seed in the
>> FUN argument function, but that may not be always the case.
>> 
>> Ivan

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595



[Rd] An idea: Extend mclapply's mc.set.seed with an initial seed value?
Prof Brian Ripley