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matlabdateplotdate-arithmetic

add incremnting seconds to time in HH:mm:ssPM format

How to add a vector of seconds to time HH:mm:ssPM in MATAB?

I usually have this nice way in Excel to convert normal number format to hour and minutes and sec. format using simple cell custom formatting, but when I put down code below in MATLAB, instead of incrementing in seconds, it adds in days!

time = 1+0:50000+0;     % sec

% To show date as plot label it should be converted from numbers to letters 
hr_matlab = time' + datenum('4:10:44 PM');
hr= datestr(hr_matlab, 'HH:MM:ssPM');

figure(222)
plot(hr,S,'-b','LineWidth',2)

I am using MATLAB2014a and don't have access to function datetime.

Solution

  • datenum converts the date to a number that represents days as whole numbers. For that reason, when you add the vector [1,2,3,...], you acturally add days to your fixed time ('4:10:44 PM').

    if you want to add it as seconds, you need to divide time in the amount of seconds per day:

    hr_matlab = (time')/86400 + datenum('4:10:44 PM');