Thanks, Greg.  I think you are right.  I did simulation one right after the
other, less than 2 seconds.

But still, it was shocking to see identical samples, which I had to throw
away.

As a rule of thumb, should I do simulation in one R console, rather than
splitting the work into 2 consoles.  I just thought it would take less time
for me, but it seems risky.

Thanks,
Mike


On Wed, Feb 20, 2013 at 6:13 PM, Greg Snow <538280@gmail.com> wrote:

> To know for sure we need to know how you are running these different R
> sessions, but here are some possibilities:
>
> The help page for "set.seed" says that if no seed exists then the seed is
> set based on the current time (and since 2.14.0 the process ID).  So one
> possibility is that 2 of the sessions are started close enough together
> that they get the same seed.  Or the difference in time and process ID
> cancel each other out.
>
> Another possibility (also mentioned in the help page) is that if the seed
> was saved in a previous session then it will be restored in the new
> session, if all the sessions are reading in the same stored session (or
> just the 2 that are the same) then they would start from the same seed.
>
>
> On Tue, Feb 19, 2013 at 6:31 PM, C W <tmrsg11@gmail.com> wrote:
>
>> Hi, list
>> I am doing 100,000 iterations of Bayesian simulations.
>>
>> What I did is I split it into 4 different R sessions, each one runs 25,000
>> iteration.  But two of the sessions gave the simulation result.
>>
>> I did not use any set.seed().  What is going on here?
>>
>> Thanks,
>> Mike
>>
>>         [[alternative HTML version deleted]]
>>
>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
>
> --
> Gregory (Greg) L. Snow Ph.D.
> 538280@gmail.com
>

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