# [Gmsh] ... electric field lines ...

mkoch@gvtc.com mkoch at gvtc.com
Fri Oct 6 16:20:41 CEST 2006

```Hi All,

I think the Plugin(StreamLines) is different from what we would need
for a Plugin(FieldLines), because of the field normalization:

StreamLines:
dx/dt = vx(x,y,z)
dy/dt = vy(x,y,z)
dz/dt = vz(x,y,z)

FieldLines:
dx/ds = Fx(x,y,z)/|F(x,y,z)|
dy/ds = Fy(x,y,z)/|F(x,y,z)|
dz/ds = Fz(x,y,z)/|F(x,y,z)|

Nevertheless, it should be possible to copy the StreamLines plugin to
a FieldLines plugin and add this normalization to it. I'll take a look
at the .CPP file later on today. However, I hope that most of the
stuff in there is in pure C, as I am virtually illiterate in C++.

Regards,

Matt Koch

----- Message from cag32 at case.edu ---------
Date: Thu, 05 Oct 2006 18:57:50 -0400
From: Christophe Geuzaine <cag32 at case.edu>
Reply-To: Christophe Geuzaine <cag32 at case.edu>
Subject: Re: [Gmsh] ... electric field lines ...
To: mattkoch at scitex.us
Cc: gmsh at geuz.org

> Matt Koch wrote:
>> Hi All,
>>
>> this seems to be a simple matter of solving the following equations
>>  for F = (Fx,Fy,Fz) as the vector (yeah right, NOTHING is EVER
>> simple):
>>
>> dx/ds = Fx/|F|
>> dy/ds = Fy/|F|
>> dz/ds = Fz/|F|
>>
>> with |F| = sqrt(Fx^2 + Fy^2 + Fz^2)
>>
>> Even a dumb Runge-Kutta approach could probably do. I might could give
>
> Isn't this pretty much what we do in Plugin(StreamLines)? There we
> solve dX(t)/dt = V, with X(0) chosen as a bunch of points in space and
> V(x,y,z) interpolated from the vector view.
>
>> it a try, but I'd need to know how to write plugins (how to
>> programmatically access fields calculated by GetDP, how to
>> programmatically draw in GMsh, and such), and perhaps get some
>> feedback from y'all on how long it might take to write a "typical"
>> plugin? Would some sort of Runge-Kutta driver or other ODE solver
>> be accessible to a plugin, or would that have to be developed from
>> scratch, or pulled in from GSL, for example?
>
> Have a look at Plugin/StreamLines.cpp in the Gmsh source code: you'll
> see that it's actually pretty simple to write a plugin.
>
>
>
>>
>> Thanks,
>>
>> Matt Koch
>>
>>
>> Christophe Geuzaine wrote:
>>
>>> Matt Koch wrote:
>>>
>>>> Hello there!
>>>>
>>>> what a wonderful program GMsh is! It takes a little while to get
>>>> used to its GUI, but once you get the hang of it, it is extremely
>>>>  useful and intuitive! However, one thing I have not been able to
>>>>  figure out yet is how to make electric field lines from an
>>>> electric field vector solution. I looked into the StreamLines
>>>> PlugIn, but that seems to only work off of a velocity field. Any
>>>> thoughts?
>>>
>>>
>>> Maybe this could be a good idea for a new plugin?
>>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>> Matt Koch
>>>> mattkoch at scitex.us
>>>> www.scitex.us
>>>> _______________________________________________
>>>> gmsh mailing list
>>>> gmsh at geuz.org
>>>> http://www.geuz.org/mailman/listinfo/gmsh
>>>>
>>>
>>>
>>
>
>
> --
> Christophe Geuzaine
> Assistant Professor, Case Western Reserve University, Mathematics
> http://www.case.edu/artsci/math/geuzaine

----- End message from cag32 at case.edu -----

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