Thanks for the suggestions - I have looked a bit closer at the code, and it appears that all the grid elements (x,y,z) where these large errors appear are those where dffts%iplw(x) == 1 .AND. dffts%iplw(y) == 1
However, there are some grid elements which meet the above criteria that do not have errors, so maybe I am not understanding something about how the FFT works? I can't think of anything else in the fft_dlay_descriptor data structure that helps narrow down further where these errors occur - any ideas? Cheers - Iain -- Iain Bethune Applications Consultant, EPCC Email: ibethune at epcc.ed.ac.uk Tel/Fax: +44 (0)131 650 5201/6555 Mob: +44 (0)7598317015 Addr: 2404 JCMB, King's Buildings, Mayfield Road, Edinburgh, EH9 3JZ The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. > -----Original Message----- > From: Paolo Giannozzi [mailto:giannozz at democritos.it] > Sent: 15 January 2010 17:41 > To: ibethune at epcc.ed.ac.uk; PWSCF Forum > Subject: Re: [Pw_forum] Errors in parallel 3D FFT > > > 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. > --- > Paolo Giannozzi, Dept of Physics, University of Udine > via delle Scienze 208, 33100 Udine, Italy > Phone +39-0432-558216, fax +39-0432-558222 > > >
