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How is "quartely" defined in the function retime?

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Hi. I am using retime to get quarterly mean data from irregularly distributed measurements:
yTT = retime(xTT,'quarterly',@nanmean);
My first measurement is on the 1st of April. The new yTT timetable has now timesteps at April, July, September, and January. My question is now are these quarterly values means of the widely used Mar-Apr-May, Jun-Jul-Aug, Sep-Oct-Nov, and Dec-Jan-Feb? Or is the April quarterly value an average of Apr-May-Jun, and so on?


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Accepted Answer

Adam Danz
Adam Danz on 29 May 2020
According to Wiki,
  • First quarter, Q1: 1 January – 31 March (90 days or 91 days in leap years)
  • Second quarter, Q2: 1 April – 30 June (91 days)
  • Third quarter, Q3: 1 July – 30 September (92 days)
  • Fourth quarter, Q4: 1 October – 31 December (92 days)
While in the Chinese calendar, the quarters are traditionally associated with the 4 seasons of the year:
The months you see are the first month within the quarter.


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Fabrice Lambert
Fabrice Lambert on 30 May 2020
Indeed. I may have misunderstood the code. Using R2020a, the relevant section in synchronize is between lines 495 and 518. The comment says "Given a choice of time step name and the min/max times of the data being synchronized, return nicely-aligned spanning time limits and the actual time step."
But then at line 514 they use timeshift to move the original tmin and tmax, so you may be right, the new time stamps will be between the two closest earlier quarters.
timeshift still doesn't define what a quarter actually is, but looking at your example it appears they use the gregorian ones.
Adam Danz
Adam Danz on 30 May 2020
You're exactly right. That section of the code shifts the starting time of the timetable to the nearest quarter and then increments by 3-months from there.
I also agree that the documentation could be clearer. If you go to the retime() and synchronize() documentation pages online and scroll to the bottom, you can give those pages a star rating and then a window will appear allowing you to give feedback. I'll make this suggestion on both pages (you could, too, if you'd like).

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