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# Re: [femm] Gradient?

- To: femm@yahoogroups.com
- Subject: Re: [femm] Gradient?
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Thu, 29 Nov 2001 15:23:16 -0500
- Organization: Foster-Miller, Inc.
- References: <9u3ul6+oieo@eGroups.com>

Vencislav wrote:

> Hello!

> How can I make Femm display gradient of magnetic field
> around magnets and surounding them objects?

> thanks,
> Vencislav

Well, the program currently doesn't display field gradients. It would be possible to write a lua script that would write gradient information to a file, which could then be plotted with some other plotting program, e.g. gnuplot. The program doesn't specifically evaluate gradient, but you could compute it numerically from within a lua script.

I'd be a bit careful using gradient information out of femm, as well--the interpolation that the program uses yields piece-wise constant flux density. The program implements a smoothing algorithm to get the flux to vary smoothly, and the derivatives of the smoothed flux density would be the gradient. The order of accuracy in the gradient would be worse than that of the field values themselves. The smoothed B-field would yield piece-wise constant gradients, and you'd want a really fine mesh to keep the level of error in check.

Dave.

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- References:
  - Gradient?
    - From: "Vencislav" <vencib@yahoo.com>

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