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Duration in double between two datenum

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I have two dates given in text format, I want to have the real duration in seconds between the two values.
The answer is -24, and I can do it parsing the strings. But does MATLAB have a function to do it nice and quick?
If I do the following the answer is not a -24 that I can use as a double:
datenum('2018-09-07 18:36:05.079')-datenum('2018-09-07 18:36:29.079')
I need this time for a Simulink simulation. For example, I might need the duration in seconds between two days.
  2 Comments
Stephen23
Stephen23 on 7 Sep 2018
"The answer is 24"
The answer is actually -24
Luis Ruiz
Luis Ruiz on 10 Sep 2018
I edited my question to match the answers.

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Accepted Answer

Stephen23
Stephen23 on 7 Sep 2018
Edited: Stephen23 on 7 Sep 2018
To get seconds simply multiply the days by 60*60*24:
>> F = 'yyyy-mm-dd HH:MM:SS.FFF';
>> D = datenum('2018-09-07 18:36:05.079',F)-datenum('2018-09-07 18:36:29.079',F);
>> D*60*60*24
ans = -24.000
  2 Comments
Luis Ruiz
Luis Ruiz on 10 Sep 2018
Edited: Luis Ruiz on 10 Sep 2018
This one seems to be the right answer, but then, does it mean that operations between two datenum values are always in days?
Stephen23
Stephen23 on 10 Sep 2018
@Luis Ruiz: yes, datenum always returns days. But the conversion to seconds is trivial, as my answer shows.

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More Answers (2)

Peter Perkins
Peter Perkins on 7 Sep 2018
If possible, don't use datenum. Use datetimes:
>> fmt = 'yyyy-MM-dd HH:mm:ss.SSS';
>> dur = datetime('2018-09-07 18:36:05.079','Format',fmt) - datetime('2018-09-07 18:36:29.079','Format',fmt)
dur =
duration
-00:00:24
>> dur.Format = 's'
dur =
duration
-24 sec
  3 Comments
James Tursa
James Tursa on 7 Sep 2018
To turn it into a double, e.g.
seconds(dur)
Peter Perkins
Peter Perkins on 12 Sep 2018
As James says, you can convert, but the point of duration is that you may not need a number. duration supports all kinds of time arithmetic. Hard to know if that's possible in your case.

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Image Analyst
Image Analyst on 7 Sep 2018
Edited: Image Analyst on 10 Sep 2018
Try the etime() function.
t1 = datevec('2018-09-08 18:36:05.079','yyyy-mm-dd HH:MM:SS.FFF')
t2 = datevec('2018-09-07 18:36:29.079','yyyy-mm-dd HH:MM:SS.FFF')
elapsedTime = etime(t1, t2) % Results in seconds.

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