When run these two commands in Matlab command line:
dateNumber = datenum('20130101', 'yyyymmdd');
dateString = datestr(dateNumber, 'yyyymmdd')
I got
dateString = 14700101
I suspect that it is a confusion between Buddhist year and Christian year because 2013-1470 == 543 (Buddhist year started in counting 543 years before Christian year). In other words, the datenum function interpreted 2013 as Buddhist year and convert it to a date number representing Christian year, 1470, but datestr function did not convert it back to Buddhsit year.
How can I configure the datenum function so that it understands 2013 as a Christian year?
Related
I want to be able to get "mmm-yy" in BigQuery. What is the best way to do this. For example "Dec-20"
Use %b-%y instead:
select FORMAT_DATETIME("%b-%y", DATETIME(Current_date()))
Format elements:
%A The full weekday name.
%a The abbreviated weekday name.
%B The full month name.
%b or %h The abbreviated month name.
%C The century (a year divided by 100 and truncated to an integer) as a decimal number (00-99).
%D The date in the format %m/%d/%y.
%d The day of the month as a decimal number (01-31).
%e The day of month as a decimal number (1-31); single digits are preceded by a space.
%F The date in the format %Y-%m-%d.
%G The ISO 8601 year with century as a decimal number. Each ISO year begins on the Monday before the first Thursday of the Gregorian calendar year. Note that %G and %Y may produce different results near Gregorian year boundaries, where the Gregorian year and ISO year can diverge.
%g The ISO 8601 year without century as a decimal number (00-99). Each ISO year begins on the Monday before the first Thursday of the Gregorian calendar year. Note that %g and %y may produce different results near Gregorian year boundaries, where the Gregorian year and ISO year can diverge.
%j The day of the year as a decimal number (001-366).
%m The month as a decimal number (01-12).
%n A newline character.
%Q The quarter as a decimal number (1-4).
%t A tab character.
%U The week number of the year (Sunday as the first day of the week) as a decimal number (00-53).
%u The weekday (Monday as the first day of the week) as a decimal number (1-7).
%V The ISO 8601 week number of the year (Monday as the first day of the week) as a decimal number (01-53). If the week containing January 1 has four or more days in the new year, then it is week 1; otherwise it is week 53 of the previous year, and the next week is week 1.
%W The week number of the year (Monday as the first day of the week) as a decimal number (00-53).
%w The weekday (Sunday as the first day of the week) as a decimal number (0-6).
%x The date representation in MM/DD/YY format.
%Y The year with century as a decimal number.
%y The year without century as a decimal number (00-99), with an optional leading zero. Can be mixed with %C. If %C is not specified, years 00-68 are 2000s, while years 69-99 are 1900s.
%E4Y Four-character years (0001 ... 9999). Note that %Y produces as many characters as it takes to fully render the year.
for my project, I need to calculate TOW (Time of week) in Simulink. I know this can be achieved through conversion of UTC time to GPS time.
I have written a simple m-file in Matlab which does the action for me in Matlab as follow:
date_gps_int = 10000*y + 100*m + d
date_gps_str = int2str(date_gps_int)
date_gps_str_to_serial = datenum(date_gps_str,'yyyymmdd')
date_str_format = datestr(date_gps_str_to_serial,'dd-mmmm-yyyy')
Num_Days = daysact('06-jan-1980',date_str_format)
Num_Weeks = Num_Days/7
TOW = Num_Weeks - 1024
My first intention was to use this as a function in simulink. But apparently because of 'datenum' and 'datestr' it is not possible, since simulink does not handle strings.
Now I am wondering if anyone can help me with this issue. Is there any way to calculate TOW from the UTC date in Matlab without using those predefined functions?
I also tried to write an algorithm for calculating number of days since '6 January 1980' and then calculating number of weeks by dividing that by 7. But since I am not very familiar with leap year calculation and I don't really know the formula for these kinds of calculations, my result differs from real TOW.
I would appreciate if anybody can help me on this.
There are three formats handled by Matlab for time: formatted date strings - what datestr outputs -, serial date - scalar double, what datenum outputs - and date vectors (see datevec). Conversion functions work with these three, and the most convenient way to convert individual variables (year, month, etc) to a date is to build a date vector [yyyy mm dd HH MM SS].
date_gps_str_to_serial = datenum([y m d 0 0 0]); % midnight on day y-m-d
date_Jan_6_1980 = datenum([1980 01 06 0 0 0]); % midnight on Jan 6th, 1980
Num_Days = date_gps_str_to_serial - date_Jan_6_1980;
Now, beware of leap seconds...
GPS time is computed form the time elapsed since Jan 6th 1980. Take the number of seconds elapsed since that day, as measured by the satellites' atomic clocks, divide by (24*3600) to get a number of days, the remainder is the time of the day (in seconds since midnight).
But, once in a while, the International Earth Rotation and Reference Systems Service will decide that a day will last one second longer to accommodate for the slowing of Earth rotation. It may happen twice a year, on June 30th or December 31st. The calculation of GPS time is wrong, because it does not take into account that some days last 86401 seconds (so dividing by 24*3600 does not work) and will advance by 1 second with respect to UTC each time this happens. There has been 18 such days since Jan 6th 1980, so one should subtract 18 seconds from GPS time to find UTC time. The next time a leap second may be added is June 2019.
I want to create a list of dates that go until the end of February. However, since the end of February changes from 28 to 29 depending on whether there's a leap year, I'm having trouble with how to consider both options.
Here's what I have so far:
date = datenum(years(i),12,01):1:datenum(years(i)+1,02,29);
This case, when run on a year that is not a leap year, ends up counting March 1st instead of ending on Feb. 28th.
Here's a little hack I came up with. You can check whether a year is a leap year quite easily by calculating the number of days between February 28 and March 1, like so:
datenum(years(i), 3, 1) - datenum(years(i), 2, 28)
Checking whether it's larger than 1 would indicate leap year. This 1 or 0 logical MATLAB convention leads to the second part of the hack: this is exactly the number of days you need to add to Feb 28: 0 if not leap year, 1 if leap year. Here, therefore, is the full hack:
date = datenum(years(i),12,01):datenum(years(i)+1,02, ...
28 + ((datenum(years(i)+1,3,1) - datenum(years(i)+1,2,28))>1) );
UPDATE / IMPROVEMENT:
Answer already accepted, but I came up with an even better solution. I didn't realize that datenum simply counts days. In this case, we can simply say that the last day of February is the day before March 1. This yields the following drastic simplification:
date = datenum(years(i),12,01):1:(datenum(years(i)+1,3,1)-1);
Datenum, for good or ill, takes negative and zero numbers. So the last day of February can be written:
datenum(2015, 3, 0)
With a comment explaining this madness, of course.
The code below gives a decimal day for one specific year.
HolidayArrayDate(2) = datenum(2012,01,16,00,00,00); %MartinLutherKingJrBirthday
I am trying to make the holiday more general for an input "dataYear" instead of specifying it as "2012". Martin Luther King Jr Birthday is the third Monday of ever year. When i provide it an input of any year 2010/2011/2012/2013/2014 through "dataYear", it should automatically choose the third Monday in January for me. How would i dot this?
Thank you!
Starting from the first day of the year, 21 days always suffice to find the third Monday. So: get serial date number for first day of the year (with datenum); get day-of-the-week for that and the following 20 days (datestr(..., 'd')); find the first three Mondays (find(...=='M', 3); and finally pick the third one and convert it into date string (datestr):
dataYear = 2012; %// input
f = datenum(dataYear,1,1); %// 1st day of year, in serial date number format
r = find(datestr(f+(0:20), 'd')=='M', 3); %// find three Mondays from that day on
result = datestr(f+r(3)-1); %// third Monday, in date string format
I would like to check whether it is Saturday and Sunday in MATLAB. I know there is a function called busday in MATLAB to check whether it is a business day but I would like to check whether it is Saturdays or Sunday respectively so that I find the corresponding Monday, which I need in my calculation.
Need some guidance on how to do this.
You need the weekday function:
http://www.mathworks.com/help/matlab/ref/weekday.html
D = '21-Dec-2012';
[DayNumber,DayName] = weekday(D)
DayNumber =
6
DayName =
Fri