bugGNU Octave - Bugs: bug #48858, datenum gives wrong results at...

 
 

bug #48858: datenum gives wrong results at daylight saving time switchover period in spring

Submitter:  Philip Nienhuis <philipnienhuis>
Submitted:  Mon 22 Aug 2016 02:45:47 PM UTC
 
Category:  Octave Function Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Duplicate Assigned to:  None
Originator Name:  Philip Nienhuis Open/Closed:  * Closed
Release:  * dev Operating System:  * Any
Fixed Release:  None Planned Release:  None
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Mon 22 Aug 2016 04:53:44 PM UTC, comment #1: 

This has been reported quite a while ago as bug #36954 and bug #37798. Closing as a duplicate.

Mike Miller <mtmiller>
Project Administrator
Mon 22 Aug 2016 02:45:47 PM UTC, original submission:  

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.

Philip Nienhuis <philipnienhuis>
Project Member

 

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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2016-08-22 mtmiller StatusNone Duplicate
        Open/ClosedOpen Closed
        Dependencies- Depends on bugs #36954

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