[Octave-bug-tracker] [bug #48858] datenum gives wrong results at daylight saving time switchover period in spring

[Philip Nienhuis]

URL:
  <http://savannah.gnu.org/bugs/?48858>

                 Summary: datenum gives wrong results at daylight saving time
switchover period in spring
                 Project: GNU Octave
            Submitted by: philipnienhuis
            Submitted on: Mon 22 Aug 2016 04:45:47 PM CEST
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Philip Nienhuis
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

Octave:

>> format long
>> datenum ('2015-03-29 02:30', 'yyyy-mm-dd HH:MM')
ans =  736052.145833333
>> datestr (datenum ('2015-03-29 02:30', 'yyyy-mm-dd HH:MM'), 0)
ans = 29-Mar-2015 03:30:00


while Matlab (r2012a) gives:

>> format long
>> datenum ('2015-03-29 02:30', 'yyyy-mm-dd HH:MM')
ans =
     7.360521041666666e+05
>> datestr (datenum ('2015-03-29 02:30', 'yyyy-mm-dd HH:MM'), 0)
ans =
29-Mar-2015 02:30:00



That Octave's datestr works correctly can be seen more clearly by filling in
Matlab's answer for 
datenum ('2015-03-29 02:30', 'yyyy-mm-dd HH:MM'):

>> datestr ( 7.360521041666666e+05, 0)
ans = 29-Mar-2015 02:30:00


AFAICS (after processing several years of 10-minute tidal observations) is
that this only happens during spring, when time changes from "winter time" to
"summer time" / daylight saving time, in the period between 01:59.59 AM and
02:59:59 AM.

IOW, applying
datestr (datenum (vdates, 'yyyy-mm-dd HH:MM'), 0)
to the following array of strings (vdates):

2015-03-29 01:30
2015-03-29 01:40
2015-03-29 01:50
2015-03-29 02:00
2015-03-29 02:10
2015-03-29 02:20
2015-03-29 02:30
2015-03-29 02:40
2015-03-29 02:50
2015-03-29 03:00
2015-03-29 03:10
2015-03-29 03:20
2015-03-29 03:30


gives

29-Mar-2015 01:30:00
29-Mar-2015 01:40:00
29-Mar-2015 01:50:00
29-Mar-2015 03:00:00
29-Mar-2015 03:10:00
29-Mar-2015 03:20:00
29-Mar-2015 03:30:00
29-Mar-2015 03:40:00
29-Mar-2015 03:50:00
29-Mar-2015 03:00:00
29-Mar-2015 03:10:00
29-Mar-2015 03:20:00
29-Mar-2015 03:30:00



I found this bug also in Octave-3.8.2.





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