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# SIMION 8.0 Issues/Bugs/Enhancements

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```Issue I372 [enhancement,high]
Define open boundaries explicitly with Neumann conditions?
See
http://www.simion.com/info/First_Uniqueness_Theorem
http://www.simion.com/discuss/viewtopic?p=948
http://www.simion.com/discuss/viewtopic?p=1402
http://simion.com/discuss/topic/1005-boundry-conditions/ ryan20100628
Description:
The following change to the "symmetry refining equations"
shown near the beginning of the "Computational Methods"
chapter of SIMION 7.0 and 8.0 manuals is suggested (davidm-200703).

Non-mirrored 2D planar PA boundaries shall be changed from

All edge points: P0 = (P1+P2+P3)/3 {top edge}   to
All edge points: P0 = (P1+P2+P3+P4)/4 = (P1+P2+2*P3)/4 {top edge}
(note: assuming P4 = P3)

The latter is the same Neumann boundary condition imposed when
mirroring is enabled.

Non-mirrored 3D and 2D cylindrical PA boundaries shall be changed
similarly.

This change seems to make little numerical difference in practice
(though perhaps further testing is needed), and it seems to put
the non-mirrored open boundaries on firmer theoretical footing.
At least, I'm not sure the current form has much theoretical
justification, though it does work very much like a Neumann
boundary in practice.

The change will also more formalize the understanding that it is
possible to define mirror planes on both left and right (X-plane)
sides of a PA since the edges are in fact Neumann boundaries,
which mirror planes behave identically to.

The change is fairly trivial to make.

Resolved in 8.1.0-TEST4 (for details, see the section titled
"Neumann boundary conditions" in the SIMION 8.1 help file.

```
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