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Re: [ESPResSo-users] have_quaternion

From: Rudolf Weeber
Subject: Re: [ESPResSo-users] have_quaternion
Date: Mon, 4 Mar 2019 13:21:28 +0100
User-agent: Mutt/1.9.4 (2018-02-28)

Hi Martin,
> I have an issue regarding the have_quaternion option for the virtual sites 
> implementation. My setup looks as follows:
> I have two particles, one of them is a Langevin swimmer, the second is a 
> dipole. The dipole is a virtual site to the swimmer. My goal is to let the 
> dipole and the propulsion force always show into the same direction. This 
> means for me, that the director of both particles should show into the same 
> direction. The have_quaternion option should, to my understanding, update the 
> orientation of the virtual particle so it always has the same orientation 
> compared to the orientation of the real particle.
> Unfortunately, as soon as I activate the have_quaternion feature, the 
> director of my virtual particle is set to [0,0,0]. I have no idea why that 
> happens and, in case it is intended, what it means.
> So the issues are:
> - Fix the orientation of directors of real and virtual, relative to each 
> other.
> - have_quaternion sets virtual director to [000].
Please retry with the current development code.
The 4.0-branch still stores the director on the particle. That might be missing 
in the virtual site update. The current code calculates the director (and 
vectorial dipole moment) from the quaternions on the fly.

Regards, Rudolf
Dr. Rudolf Weeber
Institute for Computational Physics
Universit├Ąt Stuttgart
Allmandring 3
70569 Stuttgart
Phone: +49(0)711/685-67717
Email: address@hidden

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