[aspect-devel] Progress in writing the mantle convection code Aspect

[Thomas Geenen]

why not use this interface for gsl to sprng?

http://darrenjw.wordpress.com/2010/12/14/getting-started-with-parallel-mcmc/

this will give you a proper parallel random distribution
i used it in a parallel spde code to generate the random forcing term in
parallel.

cheers
Thomas


On Wed, Oct 16, 2013 at 12:43 AM, Wolfgang Bangerth
<bangerth at math.tamu.edu>wrote:

>  Good question.  I did a few tests on Stampede and it looks like it will
>> scale reasonably well.  If we assume 1e9 particles with id+XYZ (4 doubles
>> =
>> 32 bytes) per particle, we need to broadcast ~30 GB from the root process
>> in many small packages.
>>
>
>  [...]
>>
>>
>> Each of these is the average of 100 broadcasts.  At the kind of transfer
>> rates we see above, sending 30GB of particle data would take a minute or
>> two, which would occur once during initialization.  This can be improved
>> further by intelligently sending particles only to processes that have a
>> chance of containing them (track bounding boxes at the root process).  And
>> transmission likely won't be the slowest part, but rather determining if a
>> particle is in a particular cell, which has to occur no matter what method
>> we use.
>>
>> I'll look in the literature to see if there's a better way of doing this
>> sort of thing but this seems reasonable from what I can tell.
>>
>
> How about this:
>
> Every processor has a fraction 0<=V_i<=1 of the total probability, so that
>   sum_i V_i = 1
> and V_i is the integral over the local subdomain. Let's do an all-to-all
> on these. Then, each processor draws N numbers between zero and one from a
> random number generator that is initialized in exactly the same way (easy
> to do with the RNGs from BOOST). For one of these numbers x_k, if
>   sum_{i=0}^{subdomain_id-1} V_i <= x_k <= sum_{i=0}^{subdomain} V_i
> then we need to generate a particle locally. Otherwise, we simply draw the
> next number x_k. This ensures an accurate total number of particles, and it
> randomly distributes where they are located across the subdomains. If we do
> need to create a particle on the current processor, then we do the same
> process on the current processor to find out which cell and where inside
> the cell to create the particle.
>
> I think this way you get around the communication and you get the same
> statistical properties.
>
> Best
>
>  W.
>
>
> --
> ------------------------------**------------------------------**
> ------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                 www: http://www.math.tamu.edu/~**bangerth/<http://www.math.tamu.edu/~bangerth/>
>
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