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Re: [ESPResSo-users] have_quaternion

From: Martin Kaiser
Subject: Re: [ESPResSo-users] have_quaternion
Date: Mon, 4 Mar 2019 15:34:06 +0100

> On 04.03.2019, at 13:21, Rudolf Weeber <address@hidden> wrote:
> 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
> Germany
> Phone: +49(0)711/685-67717
> Email: address@hidden

Hi Rudolf,

I tried, but I get exactly the same behaviour, with the director beeing [0,0,0].


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