[Pw_forum] Errors in parallel 3D FFT

[Paolo Giannozzi]

On Jan 14, 2010, at 11:41 , Iain Bethune wrote:

> So most of the elements have small errors (which is as expected),  
> but there
> are a large number which have very large errors (>1e-06), and I don't
> understand why this should happen.

nor do I, but it seems to me rather unlikely that the FFT used in QE  
is wrong.
Try first with a simpler system in serial execution and then try more  
complex
cases. Note that not all elements of FFTs arrays are "physical": for  
reasons
of increased speed, it is sometimes convenient to increase the first
dimension of arrays by 1

P.
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Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222