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# Re: [femm] Re: Circuits in FEMM

- To: femm@yahoogroups.com
- Subject: Re: [femm] Re: Circuits in FEMM
- From: dcm3c@aol.com
- Date: Fri, 7 Sep 2001 00:25:25 EDT

In a message dated 9/5/01 12:52:32 PM Eastern Daylight Time,
frank.e.lenning@boeing.com writes:

> Thanks Dave. What is the equation that FEMM solves for the time
> harmonic case and where does it do it in the FEMM source code?

I've put a brief note in the "files" section on the extra equation that the
program solves associated with each current constraint:
http://groups.yahoo.com/group/femm/files/currentconstraint.pdf
The source code associated with it lives (for the 2d planar case) in the
prob2big.cpp and (for the axisymmetric case) prob4big.cpp files of fkn. The
code that enforces it is sort of strewn around, because the extra equation
really gets built implictly. Only the upper diagonal of the matrix is
stored, because of the symmetry of the problem, so the extra equation gets
built by adding extra forcing terms associated with the unknown gradient to
the elements that live in the regions associated with the circuit. Look for
the comments that show where the circuit parts live (e.g. lines
78-89,294-302, 335-340 in prob2big, similar implementation in prob4big) . In
the source code, the voltage gradients are included in the vector of unknowns
right after the nodal values of potential. The voltage gradients also get
written to disk in the .ans file.
Dave.

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