Parallel output: time and processor blocks

SELFE binary state output is emitted in a directory called /outputs. This directory must exist or you will get an immediate warning from the model. Depending on your MPI configuration, the /outputs directory may exist in a central location (this is more common) or each processor may have an instance in which case you need to collect together the contents into a central location.

An example file name is 9_0000_elev.61. More generally, the file name is: [time_block]_[processor_no]_[variable_name].[fortran_unit]

Variable name

The variable name is transparent and covered in the documentation.

Time block

The time blocks start from 1 and are sequential. The model buffers and writes data occasionally. Every ihfskip time steps it opens a new time block. For instance, if the time step is 120 seconds and ihfskip = 10080 each block will be 14 days long.

1. "Neat" time lengths that will make meaningful analysis (e.g. 14 days) are usually easiest later when you postprocess.
2. Some of the output post-processing scripts will run a lot better if the length of your simulation is an even multiple of ihfskip. This can be done by altering ihfskip or the simulation length -- at the risk of lengthening the simulation a bit, the latter often produces a neater result.
3. If your simulation length is not an even multiple of the time block length, the last time block will be truncated on the last block. This will cause some minor errors and warnings in the post-processing tools. In addition, if you then restart the run it is best to repeat and overwrite the truncated block -- the post-processing tools do not work well with blocks that grow and shrink in the middle of the run.
4. Even if the output blocks match the end of the simulation very neatly, the model (at the time of writing) will open a new block that will be unused. This is odd but harmless.

Processor number

The mpi_processor number starts at 0 and represents the mpi processor id from the task that wrote the output. If your processor writes to a shared directory, the files for different processors will be collocated, but since clusters are not always set up the same way and each process is writing locally this isn't always the case. The per-processor outputs are usually gathered into a global binary. The scripts that do this are called combine_output*. Once you are done, you will have a binary file called something like 9_elev.61. The time block and the variable name remain. There is no utility for gathering the outputs in time, instead most post-processing tools are able to work with multiple files.