How to use these input files: modules/external_petsc_solver/test/tests/...?

[Wang-Yihu]

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Question

How to use these input files: modules/external_petsc_solver/test/tests/moose_as_parent.i; petsc_transient_as_sub.i; petsc_transient_as_parent.i; moose_as_sub.i ?
Recently, i'm trying to coupling external codes in MOOSE. Although #28287 suggests that maybe choosing external_petsc_solver to study is a good choice because of its hard-coded, I'm still interested in it. At least I want them to run in my PC.

My steps are as follows and I encounter errors:

1. Create an Application like https://mooseframework.inl.gov/getting_started/new_users.html

cd ~/projects
./moose/scripts/stork.sh thmbryton

2. Edit Makefile with yes for ALL_MODULES

ALL_MODULES               := yes

3. Compile it in application directory

conda activate moose
make

4. Copy and paste modules/external_petsc_solver/test/tests/moose_as_parent.i; petsc_transient_as_sub.i; petsc_transient_as_parent.i; moose_as_sub.i into the application directory
5. Run MOOSE opt with *.i

./thmbryton-opt -i moose_as_parent.i

And it returns errors:

"ExternalPetscSolverApp" is not a registered application name.
Unable to locate library archive for "ExternalPetscSolverApp".
We attempted to locate the library archive "libexternal_petsc_solver-opt.la" in the following paths:
      ../lib
Make sure you have compiled the library and either set the "library_path" variable in your input file or exported "MOOSE_LIBRARY_PATH".

First, it says: ExternalPetscSolverApp" is not a registered application name., I don't know what to do with it... Even I don't know why there is a app_type parameter in TransientMultiApp class https://mooseframework.inl.gov/source/multiapps/TransientMultiApp.html . I think TransientMultiApp class is from parent file
to drive sub file. Why does it need app_type?

[GiudGiud]

Hello

Can you you the executable in moose/modules/external_petsc_solver ? If you can build one

why there is a app_type parameter in TransientMultiApp class

The app_type lets us build smaller apps, or different apps from dynamically loaded libraries, than the current app you are using for the main solve
It is generally not required. You can use the same app for the parent and child solves most often. The only times it is required is if the child input can only be understood/ran properly by a different app

Guillaume

[Wang-Yihu]

You're right sir.
I input in the terminal in modules/external_petsc_solver/

conda activate moose
make

And then use this -opt in modules/external_petsc_solver/test/tests/

../../../external_petsc_solver-opt -i moose_as_parent.i

It really works!
You mean that app_type can make *.i files from different moose applications work together?

[GiudGiud]

Ok so by default we do not include the external_petsc_solver module in anyone s app build. I don’t think it s ever needed since it’s just an example.

Yes using app_type you can run inputs of a different app in a multiapp

[Wang-Yihu]

OK, thanks. Since I do not want to run a *.i file in another app at least for now, I do not want to implement this function. If I want to couple external codes in MOOSE, is making out codes in external_petsc_solver a good idea? I've mentioned that there're only five parts: base, mesh, petscsolver, problems, and timesteppers in this module, though there are some code from petsc I cannot understand now...
I'm trying to understand cardinal, https://github.com/neams-th-coe/cardinal , but there are too many codes...

[GiudGiud]

Cardinal is a better example than the external_petsc_solver of coupling external codes into MOOSE