How to update leap seconds

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James Tursa
James Tursa on 15 Sep 2023
Edited: James Tursa on 4 Oct 2023
The current version of MATLAB has a function to give you the leap second information that it is using. E.g.,
[T,vers] = leapseconds
T = 27×2 timetable
Date Type CumulativeAdjustment ___________ ____ ____________________ 30-Jun-1972 + 1 sec 31-Dec-1972 + 2 sec 31-Dec-1973 + 3 sec 31-Dec-1974 + 4 sec 31-Dec-1975 + 5 sec 31-Dec-1976 + 6 sec 31-Dec-1977 + 7 sec 31-Dec-1978 + 8 sec 31-Dec-1979 + 9 sec 30-Jun-1981 + 10 sec 30-Jun-1982 + 11 sec 30-Jun-1983 + 12 sec 30-Jun-1985 + 13 sec 31-Dec-1987 + 14 sec 31-Dec-1989 + 15 sec 31-Dec-1990 + 16 sec
vers = 65
But suppose you have a version of MATLAB that is not up to date with the latest leap second data. E.g., an older version of MATLAB, or maybe a recent version of MATLAB but there is a leap second announced that your version doesn't know about. I know there is a proposal to abolish leap seconds (programmers in multiple s/w packages never could seem to get this coded correctly), but what if there is another leap second announced before they officially become abolished or you have an older version of MATLAB? This link doesn't mention how to update MATLAB for this:
Is there a way for the user to update their version of MATLAB by downloading new files or updating current files or ...?
  2 Comments
Walter Roberson
Walter Roberson on 15 Sep 2023
It looks like it is getting the information from https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html
My suspicion is that when each version of MATLAB is built, that the xml files are pre-processed into a resource that is built-in. The individual files do not have enough information for the entire table, and I cannot find a copy of the .xml files anywhere in R2023b
James Tursa
James Tursa on 15 Sep 2023
Edited: James Tursa on 15 Sep 2023
Hmmm. I am writing some time scale conversion code (e.g., UTC to/from GPS), and my code has some internal tables that are easy to update for leap second info. But I also use the datetime UTCLeapSeconds time zone for this. It is easy enough to detect when my tables don't match UTCLeapSeconds and alert the user that there is a problem, but now how to update MATLAB if a problem is detected? That is the issue.
E.g., here is an easy way to convert UTC (or any time zone) to GPS:
format longg
dt = datetime('now','TimeZone',datetime.SystemTimeZone) % arbitrary sample input
dt = datetime
15-Sep-2023 21:00:02
GPS_epoch = datetime(1980,1,6,'TimeZone','UTCLeapSeconds');
if( ~isequal(dt.TimeZone,'UTCLeapSeconds') ) % needed to avoid MATLAB bug
dt = datetime(dt,'TimeZone','UTCLeapSeconds');
end
gps_time = seconds(dt - GPS_epoch)
gps_time =
1378846820.45726
And of course you can turn the duration into weeks and seconds_of_week if you want.
But this won't work if the internal UTCLeapSeconds does not know about all of the leap seconds, hence the desire to find some way to update MATLAB. I presume that if you executed this code in e.g. R2015a you will get a wrong answer because it is missing leap second info from 2016.

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Accepted Answer

Peter Perkins
Peter Perkins on 19 Sep 2023
James, there's no way for customers to update MATLAB with new leap seconds. The IERS data is built into a binary file.
The last leap second was 31-Dec-2016. R2016b came out a bit before that, but was "frozen" before the IERS declared that leap second in July 2016. I can't recall if we posted a patch, but if 16b is the version that matters, I can look to see if there's a patch. I know that many of our large customers validate a particular release and standardize on that for years at a time.
These days, we would incorporate a new leap second via MATLAB Updates. That process began sometime around R2018b, I forget exactly when. But in any case, 18b would have that most recent leap second, and no new ones have been declared, and it's anyone's guess whether or not any new ones will ever be declared (this was my guess).
Walter: "datetime() has more leap-second handling than I expected" Is there any leap-second handling that you were looking for that's not there?
  5 Comments
Steven Lord
Steven Lord on 21 Sep 2023
What was the first version of MATLAB that uses MATLAB Updates?
I believe release R2015a SP1 was the first release that had an Update release, based on selecting "I WANT TO: Get Updates" on the downloads page.
Searching the Support site for "leap second" and filtering to only show Bug Reports lists three bug reports:
That last links to another Bug Report (1196109) related to datetime arrays that doesn't specifically include the term "leap second".
I'm not sure of the answers to your other questions.
James Tursa
James Tursa on 4 Oct 2023
Edited: James Tursa on 4 Oct 2023
Here is a function to see if your version of MATLAB is up-to-date for UTCLeapSeconds. Of course, for any version of MATLAB later than R2016b there shouldn't be any problem as no new leap seconds have been announced since the end of 2016. But for 2016 and earlier versions of MATLAB this should tell you if you have a problem.
% LEAPSECONDCHECK checks MATLAB datetime UTCLeapSeconds for up-to-dateness
% Programmer: James Tursa
function lstable = leapsecondcheck
try % For later versions of MATLAB, just use leapseconds function
ls = leapseconds;
ls_MATLAB = ls.Date;
catch % For earlier versions of MATLAB, build a list from scratch
dv = datevec(now);
yr = dv(1) + 2;
ls_MATLAB = datetime([],[],[]);
k = 0;
for y = 1972:yr
for m = 1:12 % historically only 6 or 12, but check all just in case
dt = datetime(y,m,1,'TimeZone','UTCLeapSeconds');
if( second(dt - seconds(1)) ~= 59 )
k = k + 1;
ls_MATLAB(k) = datetime(y,m,1) - 1; % online tables use day-of, not day-after
end
end
end
ls_MATLAB = ls_MATLAB(:);
end
% Go get the latest data file for tai-utc.dat which has leap seconds info (this is a small file)
str = urlread('https://maia.usno.navy.mil/ser7/tai-utc.dat'); % Using urlread to accommodate older versions of MATLAB
% Construct the leap second date list from this file
f = strfind(str,'=JD');
ls_USNO = repmat(datetime(nan,nan,nan),numel(f),1);
for k=1:numel(f)
ls_USNO(k) = datetime(str(f(k)-12:f(k)-1),'Format','uuuu MMM dd') - 1; % online tables use day-of, not day-after
end
% Clip out Old UTC dates and Modern UTC epoch
ls_USNO(ls_USNO <= datetime(1972,1,1)) = [];
% Construct comparison table, where missing dates show up as NaT
ls_UNIQUE = unique([ls_MATLAB;ls_USNO]);
USNO = ls_UNIQUE;
MATLAB = ls_UNIQUE;
NaT = datetime(nan,nan,nan);
USNO(~ismember(USNO,ls_USNO)) = NaT;
MATLAB(~ismember(MATLAB,ls_MATLAB)) = NaT;
lst = table(USNO,MATLAB);
% If user just wants to display the result
if( nargout == 0 )
if( isequal(ls_MATLAB,ls_USNO) )
disp('All MATLAB leap seconds match USNO file.')
else
warning('MATLAB is missing leap seconds! (shown as NaT in the following table)');
disp('Check here for complete list of leap seconds:')
disp('https://www.nist.gov/pml/time-and-frequency-division/time-realization/leap-seconds') % day-of
disp(lst)
end
% If user wants the comparison table returned in a variable
else
lstable = lst;
end
end

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More Answers (1)

the cyclist
the cyclist on 15 Sep 2023
The file leapseconds.m calls a built-in file to get the list of leap seconds, but you can edit that file to add additional ones.
In fact, that file contains (commented-out) instructions on how to add leap seconds by "brute force".
  2 Comments
Walter Roberson
Walter Roberson on 15 Sep 2023
The commented-out instructions are for determining the list of leap seconds based upon what datetime() returns -- which implies that datetime() has been configured to already know the leapsecond rules.
datetime() has more leap-second handling than I expected, but in most places it is not clear to me what is taking care of determining leap seconds. I do see it calls upon matlab.internal.datetime.addLeapSeconds and matlab.internal.datetime.removeLeapSeconds which can tell you whether the time was within a leap second or not... but those are compiled in.
James Tursa
James Tursa on 15 Sep 2023
Edited: James Tursa on 15 Sep 2023
Thanks. I will take a look at that. I wonder if that same file is used by older MATLAB versions that don't have the leapseconds function (e.g., for their UTCLeapSeconds time zone calculations).

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