# Execution flags.¶

FARGO3D has options that can be activated at run time in the form:

./fargo3d -flag parfile


where “flag” is a suitable flag. The extensive list is:

-m:

Starting from version 1.2, merging output files is the default behavior and the -m flag is no longer needed. We have kept it for backward compatibility.

Merge. This flag is used for writing files in the form fieldn.dat instead fieldn_m.dat, with n,m integers (n is the output number, m is the process number). This flag has relevance when you work with MPI. In practice, after NINTERM time steps, you will have an output, and each processor will write its own piece of mesh on the disk. If -m flag is activated, they will write a single file with all the data inside, in the right order, as if the data had been written by a single process run.

-k:

Keep individual files from the different processes (do not merge outputs). This flag is required if the different processes output to different local disks, or if one dumps outputs including the ghost zones.

-o:

Redefine (overwrite) parameters on the command line. The following argument must be enclosed between quotes. The parameters are case insensitive. The syntax for the separators is relatively flexible. The following example shows a valid instruction:

./fargo3d -o "outputdir=/scratch/test, nx:200 Ny=34"  my_parameterfile.par


An error message is issued if the parameter does not exist, or is redefined several times. If the parameter was defined in the parameter file (rather than being implicitly set to its default value), an information string is output at run start.

-s:

Restart from separate files. This flag must to be used in the form:

./fargo3d -s n parfile


where n is the output number at which you want to restart the run. Each normal output could be used as a restart file. It works for Dat & VTK files. The output files used for the restart are separate, i.e. they have the shape fieldn_m.dat, and must have been produced by a run without the -m flag.

-S:

Restart from merged files. Same as before. It works for Dat & VTK files. The only difference is that the output files used for the restart are merged, i.e. they have the shape fieldn.dat, and must have been produced by a run with the -m flag.

+S:

Restart and expand a run along the X dimension. This is typically used to run a prior 2D calculation (radius, colatitude or Z) to enable a disk to relax toward some equilibrium state. Once this equilibrium state has been reached, the data is used to make up axisymmetric, three dimensional data cubes. Note that this is not considered as a restart inside the code, but rather a fresh start, except that the arrays are not filled with the initial condition but rather with the data at output number n, expanded as necessary in X:

./fargo3d -m initial_2D_run.par
./fargo3d +S 100 -m -o 'Nx=628' initial_2D_run.par


In the above example the 2D output number 100 is used to fill the arrays. The second run is this time 3D, as the number of zones in X (azimuth) is now larger than one. Since technically this is not a restart, the run will output its data at numbers 0, 1, etc. as for any fresh start. The flag +S naturally also works if the mesh is cylindrical or Cartesian. It can also be used to re-spawn a 1D run, so as to make it 2D (radius, azimuth).

-D:

Specify manually the CUDA device. This flag must to be used in the form:

./fargo3d -D n parameters.par


where n is an integer.

With this flag you can select manually the device where FARGO3D will run.

+D:

Specify the CUDA device file:

./fargo3d +D devfile parameters.par


where devfile is a text file which contains several lines. Each line must contain a host name (such as compute-0-34), followed by one of the three following separators:

: (column), / (slash), or = (equal)


followed itself by a device number. Example of device file:

compute-0-0: 0
compute-0-0: 1
compute-0-1: 0
compute-0-1: 1


This device file is intended for a run on two nodes (compute-0-0 and compute-0-1), each node having two GPUs (numbered 0 and 1 on each node). If the run is spawned on nodes not specified in the device file, the run will fail (technically, if the string returned by gethostname() does not match any beginning of line in the device file).

The device file can be used together with the job scheduler (such as torque or PBS) to obtain the list of free GPUs on the nodes of the job, even if the job scheduler is not GPU aware. The public distribution comes with a directory called jobs, in which you will find an example of PBS job file called devfile that parses the output of qstat to find the GPUs available.

-V:

The same as -S, but takes a .dat merged file, and makes VTK files. Useful if you want to convert some .dat files into VTK files.

-B:

The same as -S, but takes a VTK merged file, and makes .dat files. Useful if you want to convert some .vtk files into .dat files.

-t:

Timer. Very useful to follow the execution of a run and get an estimate of the time remaining to complete. If you want more detailed information, you can compile the code with the PROFILE=1 option (shortcut: make prof) and it will provide detailed information for each block of the time step. The -t flag is not required in this case.

-f:

Execute one elementary time step and exits. Useful for some automatic benchmarking (such as optimal block size determination), and also (indirectly) useful to merge the output of several processes (see Tips, Tricks, Todos and Troubleshooting.)

-0:

Set the initial arrays (either with condinit() for a fresh start, or reading an output if it is a restart), writes them to the disk, and exits. May be useful to merge prior outputs if FARGO3D has been run without the flag -m.

-C:

Force execution of all functions on CPU (for a GPU built). Obviously this flag does nothing if the executable was built for the CPU.

-p:

Instruct the code to execute a post restart hook upon loading the files from a previous output. This flag is not used in any of the files provided in the public release.

+/-# n:

Provides a numerical seed to the code, that is used for two things:

1. The numerical seed is zero padded up to six digits and appended to the name of the output directory.
2. This seed, which is accessible from any part of the code as the integer variable ArrayNb, will be used in general as a random seed for the initial conditions (condinit.c in the setup directory) or the file postrestarthook.c (but its use may not be limited to that).

In the case of a restart, the name of the output directory is changed prior to reading the data necessary of the restart, if the flag +# is used. Otherwise, when the flag -# is used, the data is read in the directory specified by the string outputdir of the parameter file or the command line, then the outputdir parameter is changed and the data is output to the new directory. This technique is very useful to spawn a large number of jobs when used in conjunction with $PBS_ARRAYID. Example: we run a master simulation in output directory out: ./fargo3d -m -o 'outputdir=out' parameters.par  We then fork the results of this master simulation by restarting it with many different random seeds: ./fargo3d -m -S 100 -# number -o 'outputdir=out' parameters.par  We use the output number 100 found in out for each of the runs (since we use the -# flag). number is either provided by$PBS_ARRAY or any shell loop index.

Finally, each of the runs can be subsequently restarted itself as follows:

./fargo3d -m -S 200 +# number -o 'outputdir=out' parameters.par


We must now use the flag +#, as it is important that run 23 seeks the data for restart in out000023 and not out.

When no restart is planned, one must use the +# flag instead of -#.