# explaining the output of datevec

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antonet on 26 May 2012
HI all,
I have the following code
numdays = datenum({'02/11/08'},'dd/mm/yy') - datenum({'09/10/11'},'dd/mm/yy')
numweeks28 = numdays / (7*4)
numweeks28vec = datevec(numweeks28)
that produces numdays =
-1071
numweeks28 =
-38.2500
numweek28svec =
-1 11 22 18 0 0
It is not clear to m e what -1 11 22 18 0 0 of numweek28svec means? For example, what is -1,11,...?
Thanks

Oleg Komarov on 26 May 2012
The 4th line of datevec() syntax is:
[Y, M, D, H, MN, S] = datevec(...)
Where it's self-explanatory that
-1 11 22 18 0 0
Y M D H MN S
Now, the fact that you're doing SomeDate - DateInFuture, determines the negative sign.
Thus,
datevec(-38.25)
says which Year, Month, etc.. is that serial date.
For intuition, supose you are 3 days Before Christ. Datevec would say you're in the Year before BC (thus -1), in the 12th month, 22nd day etc... (assuming he was born the 25th Dec).
antonet on 26 May 2012
thank you very much

per isakson on 26 May 2012
datevec interprets a double as a serial date number.
numdays = -1071 says that the first date is 1071 days before the latter.
numweek28svec = datevec( -38.2500 ) should return something 38.25 days before something
minus 1 year plus 11 month plus 22 days plus 18 hours will add up in something like -38.25 days
However, many Matlab releases before now datevec didn't handle this kind of calculation.
One year is that a year with a leap day or not. IMO one should NOT use datevec like this.
antonet on 26 May 2012
thank you per isakson