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I've been asked by someone who is using yt to analyze ARTIO data (yes! they exist!). They're interested in the distribution of star particle creation times (BIRTH_TIME in the internal code nomenclature). There is code to do a conversion to age that seems to have been borrowed from the ART frontend, but it's incomplete and incorrect for z > 0, so I'm porting over the c code that we use internally in ART(IO). That's all fine and good, but there's still a residual issue with code_units that I don't quite understand and hoping someone can quickly point me in the right direction.
ARTIO defines an attribute time_unit, which is stored in the ARTIO fileset and is the correct code_time -> seconds unit conversion at the redshift of the snapshot. The mapping from code time to physical time is non-linear, however, so a code unit defined at a different redshift cannot be simply converted to physical time in cgs using this number (which looks like what happens now).
Is there an easy way to override code_unit -> cgs (and other) unit mappings when it's a non-linear function? I can obviously create pre-converted versions of these fields (creation_time and particle_age both defined in seconds), but that doesn't prevent someone from loading ("STAR","BIRTH_TIME") and asking yt to convert it from code units to cgs, and getting the wrong answer:
i.e. yt.load("artio dataset").all_data()[("STAR","BIRTH_TIME")].in_cgs() gives nonsensical values.
Douglas Rudd Scientific Computing Consultant Research Computing Center email@example.com