Dirichlet BC attempt 3

[RemDelaporteMathurin]

Proposed changes

Attempt 3 at #602

Based on @jorgensd 's response on the fenics Discourse, I tried reimplementing the DirichletBC with time as a constant.

Users can give values as functions of x, t, and T.

Example:

F.DirichletBC(..., value=lambda x, t: 2*x[0] + t, ...)
F.DirichletBC(..., value=2.0, ...)
F.DirichletBC(..., value=lambda t, T: T + t, ...)

Building from this fairly generic DirichletBC class, we can implement subclasses like SievertsBC:

F.SievertsBC(
        subdomain=..., S_0=1.0, E_S=1.0, pressure=lambda x, t: 2*x[0] + t, species=...
    )

Which is equivalent to:

def value(x, t, T):
    pressure = 2*x[0] + t
    S = S_0 * ufl.exp(-E_S / F.k_B / T)
    return S * pressure**0.5

F.DirichletBC(..., value=value, ...)

TODO:

• Find a way to not have the DirichletBC objects updated when they don't need to to avoid performance losses

Types of changes

What types of changes does your code introduce to FESTIM?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

• Black formatted
• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (45c988f) 95.89% compared to head (33decd8) 96.65%.

Additional details and impacted files

@@             Coverage Diff             @@
##           fenicsx     #609      +/-   ##
===========================================
+ Coverage    95.89%   96.65%   +0.76%     
===========================================
  Files           10       12       +2     
  Lines          268      359      +91     
===========================================
+ Hits           257      347      +90     
- Misses          11       12       +1     

Files	Coverage Δ
festim/__init__.py	70.83% <100.00%> (+2.65%)	⬆️
festim/boundary_conditions/dirichlet_bc.py	100.00% <100.00%> (ø)
festim/hydrogen_transport_problem.py	97.74% <100.00%> (+0.22%)	⬆️
festim/boundary_conditions/sieverts_bc.py	95.45% <95.45%> (ø)

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[jhdark]

Just some minor refactoring

[RemDelaporteMathurin]

@jhdark I addressed your comments.

How about I open an issue to track progress on "only update the BC when needed" and we can merge this?

[jhdark]

@jhdark I addressed your comments.

How about I open an issue to track progress on "only update the BC when needed" and we can merge this?

Yep sounds good