# Duration in double between two datenum

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Luis Ruiz on 7 Sep 2018
Commented: Peter Perkins on 12 Sep 2018
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 CommentsShow 1 older commentHide 1 older comment
Luis Ruiz on 10 Sep 2018
I edited my question to match the answers.

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 CommentsShow 1 older commentHide 1 older comment
Stephen23 on 10 Sep 2018
@Luis Ruiz: yes, datenum always returns days. But the conversion to seconds is trivial, as my answer shows.

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
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.

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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