Environment variables or global definitions in input files?

ASPECT
1

I’m wondering - is there a way to include environment variables in ASPECT input files? I could imagine this being useful in a couple of ways - first, on TACC systems, users-specific $SCRATCH and $WORK directories are defined. Second, it is often useful to have global definitions like $R for planet radius that appear many times within function expressions in input files.

Thanks!

Max

2

Hi @maxrudolph,

I’ve wondered about this too.

As far as I know, ASPECT does not currently support general environment-variable expansion in input files. $ASPECT_SOURCE_DIR is a special case, but variables like $SCRATCH or $WORK are not automatically expanded in .prm files.

For function expressions, muparser supports Function constants, for example:

set Function constants = R=6371e3

but these are only local to a single function subsection. So R can be reused within that subsection, but not defined once globally and shared across multiple parts of the input file.

One possible idea might be to add a global constants mechanism at the .prm level, for example something like

subsection Global constants
  set Constants = R=6371e3, eta0=1e21
end

or perhaps a simpler form such as

set Global constants = R=6371e3, eta0=1e21, DATA=$SCRATCH/my_case

That could help with both repeated physical constants and machine-specific paths.

A global variable or macro mechanism for .prm files would be very useful.

Best,
Ninghui

3

@maxrudolph Interesting idea. That wouldn’t be too difficult to implement. My suggestion is to use the syntax $ENV{VAR} to query an environment variable VAR – this syntax is already used in other languages.

The right place to implement this would be in main.cc, at the bottom of the read_parameter_file() function.

Best
W.

4

Thanks! I will take a look at this and see if the implementation would be straightforward.

5

Perhaps list them where set Dimension, set End time etc live? Setting global constants sometimes avoid inconsistent parameters, which may hide bugs. :+1:

Cheers,
MM