Hello,

I wonder what is the preferred convention for direction of normal vectors throughout OOFEM. Specifically, I mean the edgeEvalNormal method in the interpolation class. In 2D, I checked all classes that overload it, and it seems a bit inconsistent, i.e.,

- FEI2dQuadLin returns an inward pointing vector (inward = inside element)
- FEI2dQuadQuad returns an outward pointing vector (outside element)
- FEI2dTrLin returns an outward pointing vector
- FEI2dTrQuad returns an outward pointing vector

Additionally, there are interpolations used for 2d line elements. I am aware that it does not make any sense to talk about inward/outward normal vectors in case of beam/truss elements, but here we have:

- FEI2dLineLin returns what would be an "outward" pointing vector (if compared to FEI2dQuadLin)
- FEI2dLineQuad returns what would be an "inward" pointing vector (if compared to FEI2dQuadQuad)
- FE2dLineHermite does not return a normal vector (probably a bug)

I have not checked the 3D interpolations, so no idea how it looks for the surface normals there.

I'm fine with either convention, but I think it should be consistent across interpolations, unless there is a valid reason to do the opposite? As of now, a call to edgeEvalNormal gives opposite vector for planestress2d and trplanestress2d elements. This affects the use of certain boundary conditions and loads (e.g. patch106 test, where the plate is under compression but the specified load in the input is positive).

I could not find the answer in the Input/Element manual, so I ask here.
Thanks for your help!