Re: OPLOT fails intermittently, any ideas?

[Paul van Delst <paul.vandelst(at)noaa.gov>]

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

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