I would like to set boundary values for the normal derivative. In the element I use this is a degree of freedom. So when I solve problems with homogeneous conditions there is no problem, but when solving with inhomogeneous conditions I get terrible results. I use the MatrixTools::apply_boundary_values function. Can someone explain what I am doing wrong?Is the degree of freedom the normal derivative at a point, or is it the mean value of the normal derivative along the edge, or anything like this? If this was the case, then you would have assigned a multiple of the correct value as boundary values.
The degree of freedom is the whole gradient at a corner.
In general, what happens if you have a problem with zero right hand side and nonzero boundary values on a mesh with uniform mesh size? Do you get a solution that is correct up to a multiplicative constant?
The solution is correct in the domain. The values at the boundary oscillate. Can I somehow fix it?
Best, Bärbel
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