Re: [eigen] Eigens Parallellism

[Gael Guennebaud <gael.guennebaud@xxxxxxxxx>]

I confirm Christoph answers, and I'd like to add that Eigen will never
exploit MPI. It's out of the scope of Eigen. On the other hand, the
use of GPU is more likely to happen, though that's not a priority yet.

You can replace your first loops with:

my_temperature.fill(std::numeric_limits < double >::quiet_NaN());

gael

On Tue, Jul 3, 2012 at 1:26 AM, Christoph Hertzberg
<chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> On 02.07.2012 19:53, Cassanova, Bill wrote:
>>
>> I am seeking a better understand of Eigen's parallelism logic....
>>
>>
>> -           My understanding is that Eigen "Knows" and understands
>> OpenMP..I believe I read somewhere that enabling OpenMP is simply a
>> matter of including -fopenmp on the compile line...Is this really all
>> there is to it?
>
>
> Yes, Eigen basically just checks whether openmp is enabled (and
> EIGEN_DONT_PARALLELIZE is not defined):
> http://eigen.tuxfamily.org/dox/TopicMultiThreading.html
>
>> -          To what degree does the code get auto-magically
>> transformed into an OpenMP directive?   For example...In the code
>> below.
>
>
> As of now, only matrix-matrix product and PartialPivLU profit from
> multithreading (see same link).
>
>
>> -          Are there any plans for the future to incorporate not only
>> OpenMP but also some MPI implementation?
>
>
> I don't know, but I don't think anyone is working on it right now.
>
>
>> -          Are there plans for Eigen to use some form of GPU
>> processing?
>
>
> Same here.
>
>> Example Code -----------------------
>> [...]
>
>
> Your code hardly uses any Eigen instructions. It uses Eigen mostly just for
> data holding which, I guess, can't profit from parallelization much.
> Of course Eigen will not prevent you from parallizing these parts yourself,
> but it won't automatically parallize your code.
>
> HTH,
> Christoph
>
>
> --
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> Dipl.-Inf. Christoph Hertzberg
> Cartesium 0.049
> Universität Bremen
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