%% Determine the Week of the Year
% Determine the week of the year using a serial date number.

N = weeknum(728647)

%
% Determine the week of the year using a character vector.

N = weeknum('19-Dec-1994')

%
% Determine the week of the year using a datetime array.

N = weeknum(datetime('19-Dec-1994','Locale','en_US'))

%
% The first week of the year must have at least four days in it. For example, January 8, 2004 was a Thursday. The European standard is used because the first week of the year is the first week longer than three days.

weeknum('08-jan-2004',1,1)

%
% You can also use weeknum with datenum.

weeknum(datenum('01-Jan-2004'):datenum('08-Jan-2004'))

%
% The default start day of the week is Sunday. Every day after, and including the first Sunday of the year (04-Jan-2004), returns 2 denoting the second week. In this case, the first of week of the year started before January 1, 2004. You can also use weeknum with datenum and specify a D value of 5 to indicate that the weeks start on Thursday.

weeknum(datenum('01-Jan-2004'):datenum('08-Jan-2004'),5)

% The first week of the year that has four or more days, based on the specified start day, is considered week one (even if this is not the first week in the calendar). Any day falling in (or before) this week is given a week number of 1.
% Copyright 2012 The MathWorks, Inc.