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Re: [ESPResSo-users] problem with magnetic particle system

From: Juan Jose Cerda
Subject: Re: [ESPResSo-users] problem with magnetic particle system
Date: Thu, 16 Aug 2012 12:19:14 +0200 (CEST)


        The error about "dipoar fft - Complex value is not zero" should never 
ever occur. It means the Fast Fourier Transform is not doing its job properly 
or something is not properly done during the P3M process. Due to the nature of 
the transforms, one should never get a complex part for the forces, it that 
happens it means that either the FFTW is faulty or somebody touched something 
in Espresso  that should not have been touched, like asignment functions, etc. 
It should work fine even for 1 single particle. Probably the error is such that 
when many particles exist it almost cancels out, so the complex part is small 
enough as to not be stopped by the "If" that controls if the message about 
Complex value should be displayed or not, which as far as I remember only will 
stop the program in the complex part goes up beyond 1/10**6. Nonetheless, if 
the error occurs, I am not sure the program is computing things properly, the 
effects of having an error like that can go from nothing to something quite 
severe, and the magnitude of the effect can depend on the relative position and 
orientation of the dipoles.

         The other questions, Rudolf answers were fine. Best wishes,


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