[timeseries] integer division or modulo by zero

[lvankampenhout]

I'm attempting to make timeseries of some 1-year test run that I did on an external machine. I'm using one node with 24 cores and run into the following error message:

integer division or modulo by zero

I was able to trace this back to the function divide_comm() in cesm_tseries_generator.py where there is the following code:

    min_procs_per_spec = 36
    size = scomm.get_size()
    rank = scomm.get_rank()

    if l_spec == 1:
        num_of_groups = 1
    else:
        num_of_groups = size/min_procs_per_spec
(...)
        temp_color = (rank % num_of_groups)+1

In my case l_spec equals 17 so the number of groups is 24 divided by 36, which is rounded down to 0.

I imagine the solution could be to either raise a helpful error message ("number of cores must >= 36") or to remove the magic number 36, or both.

[bertinia]

@lvankampenhout - the decision to hardcode the min_procs_per_spec = 36 is based on optimizing
the single variable timeseries generation for the CMIP6 experiments on cheyenne. We might be able
to make this setting an XML variable so it's not so restrictive to just NCAR machines. Thanks for the
bringing this up.