fix: enable proper running of backward dispersion models #82
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The duration is computed as the difference between the start and end times. If the start time is after the end time, the duration is already negative, so we don't need to prepend a "-" to it or we have a double negative before the duration value and HYSPLIT crashes.
AlFontal
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This addresses #81, and also could be considered to address #66.
Basically, there were 2 really small errors that made the logic of running backwards dispersion models not work.
For starters, the
run_modelfunction has a hardcoded 'forward' parameter, so no matter the direction specified inadd_dispersion_params, thehysplit_dispersionfunction always received 'forward' as the parameter. This is fixedin commit caead2f.
Second, the
add_dispersion_paramsfunction has nodurationparameter. The value ofdurationthat is passed ontohysplit_dispersionis computed by the difference in hours between start_time and end_time:splitr/R/run_model.R
Line 51 in 4485112
In a backwards model, the
end_timeis before thestart_time, so this variable takes negative values.When writing the CONTROL file, however, there is an ifelse clause that prepends a '-' to the duration value. In the case of an already negative value, this writes a line with --duration, leading to a faulty CONTROL file that HYSPLIT doesn't accept and it just doesn't run. Removing the ifelse clause seems to work and is what I did in d4ca419.
It would be also nice to add some examples on how to run backward dispersion models, as there is none as of now.
I think that without this PR, a hacky way of running backward dispersion models is to simply use an
end_timethat is earlier than thestart_timeby as many hours as is desired, and then simply inputforwardin the direction parameter. This will write a negative duration value to the CONTROL file and HYSPLIT will read it and run it in backward mode anyway.I am rather unfamiliar on R package development as I am mainly a python developer, so I am pretty sure this PR might need several extra steps to make it workable.