just to complete the information, this check is done in the good_fft_dimension function in Modules/fft_scalar.f90 stefano
Stefano de Gironcoli wrote: > Dear Timo, > due to memory access conflicts for certain architectures (cray was > one of these) FFT routines were significantly slower if some of the > nrx1,nrx2,nrx3 (nr1 in scalar and nr3 in parallel executions) was a > multiple of 2 while obviously nr1,nr2,nr3 are best when they are powers > of 2. It was therefore convenient to have the flexibility to set > nrx1=nr1+1 (or nrx3=nr3+1) when nr1(nr3) was even. > Now this is not anymore the case on most machines but the distinction > between nr? and nrx? remains and in some case it is still useful. > Best regards, > Stefano de Gironcoli > > Timo Thonhauser wrote: > >> Dear Developers, >> >> What is the difference between nr1, nr2, nr3 and nrx1, nrx2, nrx3 >> in the code? For all practical purposes they always seem to be >> the same. >> >> In PW/pwcom.f90 we find: >> >> nr1, &! fft dimension along x >> nr2, &! fft dimension along y >> nr3, &! fft dimension along z >> nrx1, &! maximum fft dimension along x >> nrx2, &! maximum fft dimension along y >> nrx3, &! maximum fft dimension along z >> >> But when would nr1 differ from nrx1? >> >> Thanks a lot! >> Timo >> >> >> > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
