`TXTExport` produces duplicates

[KulaginVladimir]

As highlighted by @rekomodo on discourse, TXTExport produces duplicates in the output file, what may confuse a user.

Some suggestions from @RemDelaporteMathurin to improve this behaviour:

I guess the internal FESTIM process should be:

1. if there is only one material (or no conservation of chemical potential) then project to CG instead of DG
2. If there are interfaces, since TXTExport is only used in 1D, project to DG but only keep the duplicates where there are interfaces (based > on the materials border argument)

[RemDelaporteMathurin]

I think to start with we could at least make sure that values in the txt file are sorted by x

[KulaginVladimir]

@RemDelaporteMathurin

If there are interfaces, since TXTExport is only used in 1D, project to DG but only keep the duplicates where there are interfaces (based > on the materials border argument)

Based on your recent example , such filtering might be more complex.

[RemDelaporteMathurin]

Based on your recent example , such filtering might be more complex.

Yes for traps funny things could happen but I believe we should still do this as I don't expect it would drastically alter the profile

[KulaginVladimir]

@RemDelaporteMathurin

If there are interfaces, since TXTExport is only used in 1D, project to DG but only keep the duplicates where there are interfaces (based > on the materials border argument)

if vertices of a mesh do not match the interfaces (borders), shall we try to keep duplicates near the interfaces?

Say:

model.materials = [
    F.Material(
        id=1,
        D_0=1,
        E_D=0,
        S_0=1,
        E_S=0,
        borders=[0,0.5]
    )
    F.Material(
        id=2,
        D_0=1,
        E_D=0,
        S_0=2,
        E_S=0,
        borders=[0.5,1.0]
    )
]

model.mesh = F.MeshFromVertices(
    np.linspace(0, 1, 30)
)

The closest vertices to the interface at x=0.5 are x=0.48275862 and x=0.51724138

[RemDelaporteMathurin]

1. We shouldn't condone this behaviour from users. Of course FESTIM would run but we should maybe throw a warning "vertices don't match interfaces" or something
2. if users still decide to do this for whatever reason, then we only keep the duplicate where the "fenics" interface is. I guess it's the closest vertex.

So in your example, we could do something along the lines of:

for vertex in vertices:
    if not isclose(vertex, interface_x):
        # remove duplicate

[KulaginVladimir]

I think the first point can be addressed in a separate issue.