Edit to documentation. State Neumann (natural) boundary are implicitly handled

Hi all,

I’ve seen a few posts in the past asking about implementing Neumann boundary conditions, especially homogeneous neumann boundary conditions in FreeFEM++.

I think it would be helpful to explicitly state somewhere that, since Natural boundary conditions vanish in your variational formulation, FreeFEM++ implicitly assumes any boundaries you don’t label are neumann.

Additionally, it might also help to describe how to implement Robin boundary conditions, where one implements it like:

If Th is a 3D mesh

\partial u / \partial n + g(x,y,z) = 0 on Gamma_1

You just put in

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