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Re: [ESPResSo-users] have_quaternion

From: Martin Kaiser
Subject: Re: [ESPResSo-users] have_quaternion
Date: Tue, 5 Mar 2019 10:05:34 +0100

> On 04.03.2019, at 15:59, Rudolf Weeber <address@hidden> wrote:
> Hi Martin,
> On Mon, Mar 04, 2019 at 03:34:06PM +0100, Martin Kaiser wrote:
>>>> 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.
> The relative orientation of the virtual site and the base particle is 
> crontrolled by the virtual sites 
> vs_quat
> property. If you want co-alignment, you have to set it to (1,0,0,0), which is 
> the identity for quaternions.
> The vs_quat-property defaults to (0,0,0,0), which results in a 0-director and 
> q0-quaternion on the virtual sites if have_quaternions is true.
> I had a look at the testcase, and think that the current implementation is 
> working, once vs_quat on the virtual site is set.
> Regards, Rudolf

My bad! I misunderstood vs_quat. Implemented it now and initial tests look good.
Thanks for the help.


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