Guide for new users and developers

For new users

see Installation notes for instructions for installing DALES on different systems / machines. Always make sure that required libraries are not only loaded, but also available for use. This means that on supercomputers they shall be loaded with command module load <NAME> and on personal computers the location of libraries shall be part of the $PATH environment variable.
The compiled program is in general not portable from one machine to another. For a new machine, compile again on that machine.
see Quirks for problems with specific systems and versions.

DALES runs that are even slightly different will diverge and become more and more different over time.
Parallel runs, especially with more than one node are not bitwise reproducible, because MPI does not guarantee bitwise reproducibility (probably the reduce operations which can happen in different order).

git and GitHub are used for DALES development. See this Software Carpentry course for git basics. Especially, learn about
- git clone (download DALES from github to your computer)
- branches (different "versions" of the DALES code, for example for developing a specific function)
- forking (make a copy of the DALES repository to your own GitHub account)
Avoid distributing DALES source code outside git, e.g. by email. It's hard to get the code back into git. If you want to send a version to someone else, make a new branch (in your own fork) for it, and send the link.
When changing the official version: we don't want surprise changes to the default behavior (exceptions: fixing bugs). New features should in general be introduced with namelist flags to turn them on, and the default should be the old behavior.
Prefer netCDF output over ASCII (netCDF is standardized, more robust, better tools available, easier for others to process).
DALES should work with multiple Fortran compilers. gfortran and intel are most used at the moment. Automatic tests with GitHub actions, which verify that the code compiles with multiple compilers are in development.

DALES can be run in parallel using MPI. The domain is split in nprocx * nprocy tiles in the horizontal direction. Each tile contains imax * jmax * kmax grid points. The whole domain contains itot * jtot * kmax grid points.
index ranges for the 3D fields are (2:i1, 2:j1, 1:kmax) for historical reasons. i1 = imax+1 and j1 = jmax+1.
Ghost cells are added at the edges of the 3D fields of each process, and contain values copied from neighboring tiles. ih and jh are the number of ghost cells in the x and y directions. Generally 1 <= i1,j1 <= 3, depending on the advection schemes used. A 3D field including ghost cells is indexed like this: allocate(thl0 (2-ih:i1+ih,2-jh:j1+jh,k1)). The "proper" grid points are in the range (2:i1, 2:j1, 1:kmax), and ih or jh ghost cells are added on each side in the horizontal directions.
warm starts should be bitwise exact - after a restart the model should continue as if the restart never happened. But see the note of reproducibility with MPI above.
field naming: thl0 is the thl value at the current (sub)time step, thlm is the value at the beginning of the full step, and thlp is the tendency calculated for the current time step.
the top level file calls procedures for different physical processes and statistics, each procedure keeps track of when it should run, tnext_...

the startup order is fragile, be careful if re-ordering
Fortran doesn't allow circular module references
time is counted both with floating point number of seconds, and integer number of milliseconds.