[Pw_forum] The -D__USE_3D_FFT option in PW

[Paolo Giannozzi]

On Wed, 2014-01-22 at 12:05 +0000, Paul.Caheny at uk.fujitsu.com wrote:

> Is there any documentation about the -D__USE_3D_FFT option within
> Quantum Espresso PWscf? I couldn’t find any in the various manuals.

unfortunately there isn't any, but not much is actually needed. 
This option was introduced to have some degree of parallelization
available on an old, fast but rather peculiar machine, without 
writing a parallel 3d FFT (which requires interfaces from QE to 
1D and 2D Fourier Transforms using machine optimized libraries).
(Many) Years later it turned out to be useful also for GPUs. 

You can use -D__USE_3D_FFT in conjunction with your favorite FFT
library, as long as an interface from QE to 3D library FT exists.

Paolo


>  In particular I’m interested to know whether this option is
> significant only for use with the internal FFT code provided with
> Quantum Espresso or also when using an external library for FFT (e.g.
> MKL). Any other information about the purpose/applicability/trade-offs
> involved in this option would also be very useful. 
> 
>  
> 
>  
> 
> Thanks,
> 
>  
> 
> Paul.
> 
>  
> 
>  
> 
> ---
> 
>  
> 
> Paul Caheny
> 
> Researcher
> 
> Technical Computing Research
> Fujitsu Laboratories of Europe Ltd (FLE)
> 
> phone: +44 (0) 20 8606 4529
> 
> e-mail: Paul.Caheny at uk.fujitsu.com
> 
> web: http://www.fujitsu.com/emea/about/fle/
> 
>  
> 
> 
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-- 
 Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
 Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
 Phone +39-0432-558216, fax +39-0432-558222