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Explanation of the folder structure of Lethe
The folder structure of Lethe is relatively complex. Once you have cloned and compiled Lethe, it is normal that you might be confused as to the meaning of the various folder in the cloned directory (the source) or in the build folder. This section of the wiki aims at demystifying these elements.
The source folder is the folder which has been cloned from github. At the top of the source folder, the following structure is present:
/applications/applications_tests/contrib/includes/logo/prototypes/sources/tests
In what follows, we explain the content of each folder and the logic behind this complex structure. We explain the folder not in alphabetical order but in a more "logical" order...
Lethe is designed to contain a number of solvers for single or multiphysics problem. These various solvers take the form of multiple executables which are named applications. They are stored in the /applications folder.
Each application is housed in its own separate folder. For example, the folder /applications/gls_navier_stokes_2d contains the source which instantiates the 2D version of the GLS Navier-Stokes solver, whereas the /applications/gls_navier_stokes_3d folder stores the source which instantiates the 3D version of the GLS Navier-Stokes solver.
In Lethe, solvers are minimal application with only a main file. They contain little source code (generally < 100 lines). Their only goal is to instantiate the solver classes with the appropriate dimension of the problem. Since all of Lethe solvers are templated for the dimension of the problem (int dim), the same source code is re-used in both 2D and 3D. Applications are made to be comprehensive. They are fully controlled from text files (.prm and eventually .json).
The /applications_tests folder contains the functional tests for the applications. These tests are grouped in folders which correspond to the name of the application. For example, the folder /applications_tests/gls_navier_stokes_2d folder contains multiple tests for the GLS Navier-Stokes 2D solver. Each test is two or more files and is identified with a single prefix. It must necessarily contain a ".prm" file, which is the parameter file that is used to launch the test. It must also contain a ".output" file, which is the expected output of the solver. Additional file may be present if the test it to be ran with multiple processors combination or if the test requires a mesh file.
For example the cylinder_gls test is made of three files : cylinder_gls.output, which is the expected output, cylinder_gls.prm, which is the parameter file used to control the simulation (with the appropriate boundary conditions, etc.) and the cylinder_structured.msh file which is a GMSH mesh that is required for the simulation to run.
You may notice that some outputs are preceded by a mpirun=2 prefix. For example, the mms-2d_gls.mpirun=2.output file. This additional prefix indicates that the test will be run with two processors. If this prefix is not present, the test will always be run with a single processor. To ensure enhanced compatibility with the CI, tests should not use over 3 processors.