Fair enough.
Thanks!
On Nov 17, 2008, at 1:06 PM, Eric Firing wrote:
> vschmidt wrote:
>> I'm hoping you can help me confirm/deny a bug in pylab's date2num()
>> function. My assumption (this may be wrong) is that this function
>> is meant to be
>> compatible with the MATLAB function date2num(). However, in ipython
>> I can
>> execute:
>> ---------
>> import datetime
>> import pylab as p
>> dts = datetime.datetime.now()
>> serialts = p.date2num(dts)
>> print dts
>> 2008-11-16 12:03:20.914480
>> print serialts
>> 733362.502325
>> ------------
>> If I then copy this serialts value into MATLAB I get:
>> ----------
>> datestr(733362.502325)
>> 16-Nov-2007 12:03:20
>> ----------
>> Note that the year is off by one.
>
> Evidently date2num was designed to be similar, but not identical, to
> Matlab's datenum. (The difference might have been inadvertent.)
> Matlab's documentation says,
>
> A serial date number represents the whole and fractional number of
> days from a specific date and time, where datenum('Jan-1-0000
> 00:00:00') returns the number 1. (The year 0000 is merely a
> reference point and is not intended to be interpreted as a real year
> in time.)
>
> And mpl's says,
>
>
> return value is a floating point number (or sequence of floats)
> which gives number of days (fraction part represents hours,
> minutes, seconds) since 0001-01-01 00:00:00 UTC
>
> So they simply have a different origin. I find calendars endlessly
> confusing, and I make no attempt to delve into them; but I dimly
> recall that there is a year 1, but there is no year 0, so perhaps
> that is an advantage of the mpl version--not that it should matter
> in practice.
>
> I think the conclusion is that this sort of date number should be
> considered suitable for internal use only, and not used as an
> interchange format; for going from one software system to another,
> one must use a genuine standard supported by both.
>
> Eric
>
>
------------------------------------------------------
Val Schmidt
CCOM/JHC
University of New Hampshire
Chase Ocean Engineering Lab
24 Colovos Road
Durham, NH 03824
e: vschmidt [AT] ccom.unh.edu
m: 614.286.3726
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