Check for obstacles instance in phi.physics.fluid.apply_boundary_conditions

[rcremese]

Hello, I'm kind of new using PhiFlow so I might do mistakes. But, while trying to implement a very simple 2D diffusion equation with obstacles, I faced some problems.

• First, it's hard from the documentation to understand how to use the GeometryMask class. For exemple, figuring out what the @ symbole is used to in the creation of an obstacle mask is hard to understand from the API documentation (ex: obs_mask = SoftGeometryMask(obstacle.geometry, balance=1) @ velocity)

• Second, there is no type checking in the apply_boundary_conditions function for the input variable, leading to a strange TypeError: 'Obstacle' object is not iterable when calling the function with only one istance of an Obstacle instead of a list of obstacles. Handling the case where there is only one obstacle might be usefull. Otherwise, a simple type check assert isinstance(obstacles, (tuple, list)) would do the job.

• Third, why do Obstacle and apply_boundary_conditions are bounded to the physic.fluid submodule and not accessible from the flow module ? Boundary conditions and obstacles can be applied outside of a CFD problem, isn't it ?

Nevertheless, thank you for your work on all of this, I'm very existed to use your package to implement PDE with JAX !

[holl-]

Thank you for your feedback!

1. The @ operator is being phased out in 2.3. You can already replace it by arg1.at(arg2). I'll revisit the documentation of the geometry masks.
2. Good idea, I've pushed this to 2.3-develop. It will now also accept single Geometry or Obstacle values.
3. Obstacles specifically are only used by the fluid module. Other modules use Geometry. Obstacles extend Geometry by a velocity vector and rotation speed which only makes sense in fluid-like settings.

If you run into any other strange behavior or missing documentation, let me know!

[holl-]

By the way, you can install 2.3-develop by running

pip install --upgrade git+https://github.com/tum-pbs/PhiFlow@2.3-develop

[rcremese]

Thank you for your quick reply. Now, I better understand what the purpose of Geometry and Obstacle are. I'll see if i need to use the 2.3 version. Thanks again.