Calmonths issues with February

What is going wrong here?

Shifting to the month end works fine for this example:

t0 = datetime(2016,1,1);t1 = dateshift(t0,'end','month')+calmonths(1:3)
t1 = 

     29-Feb-2016   31-Mar-2016   30-Apr-2016

But we do not get the month end when starting in Feb 2016:

t0 = datetime(2016,2,2);t1 = dateshift(t0,'end','month')+calmonths(1:3)

t1 = 

     29-Mar-2016   29-Apr-2016   29-May-2016

I first thought that this is an issue of leap year but the same problem occurs for 2015.

But then again, it works for March:

   t0 = datetime(2015,3,3);t1 = dateshift(t0,'end','month')+calmonths(1:3)

t1 = 

     30-Apr-2015   31-May-2015   30-Jun-2015

What's the issue?

Answer 1

[Walter Roberson]

January and March have 31 days, so "1 month" relative to them is more clearly "last day of February" or "last day of April". But February has 29 days in 2016, so "1 month" relative to February 29 could mean March 29 instead of March 31. I bet if you were to try starting from the last day of April (the 30th) that it would show one month later to be May 30th instead of May 31.

I do not know the solution except perhaps to use calendarDuration() more directly.

[Walter Roberson]

Yes, that makes sense.

Answer 2

[Björn]

I found the answer: The term unit of a month is a bit ambigiuous. But going to the end of a month is not controversial... Therefore, shift teh date first to any day next month and then go to the end of the month:

t0 = datetime(2016,2,2);

t1 = dateshift(t0+calmonths(1:3),'end','month')

t1 =

   31-Mar-2016   30-Apr-2016   31-May-2016