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*To*: Larry Bleau <bleau(at)umtof.umd.edu>*Subject*: Re: OPLOT fails intermittently, any ideas?*From*: Paul van Delst <paul.vandelst(at)noaa.gov>*Date*: Mon, 16 Jul 2001 16:26:10 -0400*Newsgroups*: comp.lang.idl-pvwave*Organization*: CIMSS @ NOAA/NCEP*References*: <01071616120190@umtof.umd.edu>*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:25704

Larry Bleau wrote: > > >It depends. It could be that every couple of days the values get *just* a little too big > >for their difference (epoch-base_epoch) to "fit" in a single precision format, hence the > >apparent intermittent failure. You only have 6 or 7 significant digits, e.g. > > > >IDL> x=8348374.3947d0 > >IDL> x2=8348374.3954d0 > >IDL> print, float(x2)-float(x) > > 0.00000 > >IDL> print, float(x2-x) > > 0.000700000 > > Good example in the abstract, wrong in this particular case. We're doing a 4 > hour plot. The epoch time is in seconds. That means over the course of the > plot the difference between firrst and last x-values will be 14400. We have no > problem distinguishing these times on other plots. Indeed, the only problem we > had with the single vs. double precision was labelling the x-axis: using the > unscaled x values the time axis would be labelled 1100, 1159, 1300, 1359, etc. > In other words, we'd sometimes be off 1 minute (numeric value of 60). Once we > went to scaling (just subtracting a constant) the labelling problem was fixed. > > This is a different problem, long lasting, just doesn't happen very often. O.k. Well, then you have a mighty weird error! I'm sure someone out there will have another idea. I'll post this to the ng so others will know it wasn't a precision problem. (Crap, I just reread your original email where you specifically mention this! Man! Sorry for the run-around) > Once we had this problem when there really wasn't any data for that time > period: there was a gap in the data sent from the satellite. I checked that > first thing, though, and while there is a 1-hour data gap, we still have 3 > hours of data; we'd need a 4-hour gap for that to be the cause. paulv -- Paul van Delst A little learning is a dangerous thing; CIMSS @ NOAA/NCEP Drink deep, or taste not the Pierian spring; Ph: (301)763-8000 x7274 There shallow draughts intoxicate the brain, Fax:(301)763-8545 And drinking largely sobers us again. Alexander Pope.

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