datenum using lunar calendar question

i want using lunar calendar in matlab

and want plot my tide data and using lunar calendar be my timeseries

but lunar calendar sometime have 13 months(leap year)

a leap year in the lunar calendar may have around 380 day

when i use datanum meet 13 months

corresponding time present NAN

How can I include 13 in my timeseries as well

attached is my time and water level information

A column is normal time (Gregorian calendar)

B column is lunar calendar

C column is water level data

Thanks in advance!

Answer 1

[Ashutosh Thakur]

Hi Peter,

I can understand that you want to plot your tide data with respect to lunar dates. Also the data you have contains NaN values.

I can suggest an algorithm to approach this issue:

• First try to clean the data by treating the NaN values. NaN values can be handled using many ways such as removing them, taking average of values etc. It is upto you to decide how to handle NaN values.
• Second is to create a Custom Mapping function as MATLAB inbuilt functions work on gregorian calendar. To create a custom map you have to decide on the number of months in a leap year, number of days in a month, cycle of a leap year etc and based on that try to convert gregorian date to lunar one. I have also provided a sample code to handle the same.
• Third, is now to plot these data with respect to water levels by converting the final resultant data into "timeseries" data.

Below is the pseudocode for custom mapping of gregorian to lunar, this code may not handle all the cases and further modification may be required based on the requirements:

function lunarDate = gregorianToLunar(gregorianDate)
    % Define the start date of the lunar calendar in Gregorian terms
    lunarStart = datenum(2000, 1, 1);  % Example start date (January 1, 2000)
    
    % Define the number of days in each lunar month (for simplicity, all the same)
    daysInLunarMonth = 29.53;  % Average number of days in a lunar month
    
    % Calculate the number of days since the start of the lunar calendar
    daysSinceStart = gregorianDate - lunarStart;
    
    % Define the lunar cycle (for example, every 3 years is a leap year)
    lunarCycleYears = 3;
    daysInLunarYear = 12 * daysInLunarMonth;
    daysInLunarLeapYear = 13 * daysInLunarMonth;
    
    % Calculate the current lunar year and the day within that year
    cyclePeriod = lunarCycleYears * daysInLunarYear + daysInLunarLeapYear;
    cyclesSinceStart = floor(daysSinceStart.Day / cyclePeriod);
    dayWithinCycle = mod(daysSinceStart.Day, cyclePeriod);
    
    % Calculate the number of leap years that have passed in the current cycle
    leapYearsPassed = floor(dayWithinCycle / (lunarCycleYears * daysInLunarYear));
    if leapYearsPassed >= lunarCycleYears
        leapYearsPassed = lunarCycleYears - 1;
    end
    
    % Calculate the day within the current (leap) year
    dayWithinYear = dayWithinCycle - leapYearsPassed * daysInLunarYear;
    
    % Calculate the current lunar year
    lunarYear = cyclesSinceStart * lunarCycleYears + leapYearsPassed;
    
    % Calculate the current lunar month and day
    lunarMonth = ceil(dayWithinYear / daysInLunarMonth);
    lunarDay = mod(dayWithinYear, daysInLunarMonth);
    if lunarDay == 0
        lunarDay = daysInLunarMonth;
    end
    
    % Construct the lunar date as a string or a structure
    lunarDate = struct('year', lunarYear, 'month', lunarMonth, 'day', floor(lunarDay));
end

Please take reference from the following documentation links for the reference:

• https://www.mathworks.com/help/matlab/data_analysis/missing-data-in-matlab.html
• https://www.mathworks.com/help/matlab/date-and-time-operations.html

I hope this helps you!

Thanks.