Parameters: Use AMReX Parser

[ax3l]

Use the advanced right-hand-side parser of AMReX to read user parameters in inputs files. Enable constants, temporary variables, reuse of parameters, and simple mathematical expressions.

Examples: Use Parser Where Sensible.

• depends on AMReX: development #791
• depends on AMReX: development #796

[cemitch99]

Do we really want to change all of the existing examples? Couldn't this cause some confusion to users? It might be better to have just one example to illustrate this feature.

[ax3l]

I added it whenever it made sense so people come definitely across it. I hope I did not add it in confusing places, can revert a few where it is complicating the logic ofc.

[cemitch99]

Just one question/comment about the examples.

[ax3l]

There is some funny behavior for queryAddWithParser/queryWithParser that throws off the Python tests... Behaves somehow like get or so....

Segfaults here

[WeiqunZhang]

I think the issue with python is ParmParse::Initialize (called by amrex::Initialize) has not been called when ImpactX::init_grids is called.

[WeiqunZhang]

We could try to make amrex::ParmParse more robust so that queryWithParse would work even without ParmParse::Initialize. But it may not be that easy to make it thread safe.

[WeiqunZhang]

Nevertheless, if we assume queryWithParser (before ParmParse::initialize is called) is not used inside omp parallel, it's easy to fix.

[WeiqunZhang]

However, it may not make sense to use queryWithParser if ParmParse has not been initialized. For example

foo.x = 1
foo.y = foo.x

does not work as expected if foo.x and foo.y are not in the ParmParse database.

[WeiqunZhang]

AMReX-Codes/amrex#4291 I did the FODO.py.run test, it seems to work with the amrex PR.

[ax3l]

Could I call ParmParse::initialize before amrex::Initialize to make this example work?
#792 (comment)

We def use ParmParse quite a bit before AMReX init (WarpX: dim selection; ImpactX: configuration, ...).

What actually happens in MPI contexts if we do that? Usually, ParmParse reads files only from the I/O rank, and in that case...?