How to preserve nanosecond precision in datetime calculations (for large numbers)
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Hi, I am working with datetime variables with nanosecond precision. I am trying to maintain this precision throughout the calculations, but I lose the precision because the precision of the numbers exceed double precision (for large numbers). For example, 1294871257.002060945 seconds has 3 additional digits more than double precision that I need to preserve in the calculations. I realized that I cannot use the vpa function on a datetime variable. Are there any suggestions on how to handle this? The example script below shows the loss of precision in the calculation by outputing the decimal portions of the original and final numbers.
dt=1294871257.002060945; % nanosecond precision for a large number that exceeds double precision.
epoch = datetime(1980,1,6,'TimeZone','UTCLeapSeconds'); % define the epoch reference time in UTC (and has 0 seconds)
DtUTC = epoch + seconds(dt); % add the duration to the reference time
Time_vec=datevec(DtUTC); % converts final datetime value to a 6-element vector (Y,M,D,H,M,S)
sprintf('%.9f',dt-floor(dt)) % decimal part of original number of seconds
sprintf('%.9f',Time_vec(6)-floor(Time_vec(6))) % decimal part of calculated number of seconds
Steven Lord on 11 Nov 2021
Start off with the time as a symbolic object.
If you don't and just start with dt as a double you've already lost.
Now split dt into the integer part and the fractional part symbolically.
frac = dt - floor(dt);
whole = dt - frac;
Finally add whole and frac separately to your epoch.
epoch = datetime(1980,1,6,'TimeZone','UTCLeapSeconds');
DtUTC = epoch + seconds(double(whole)) + seconds(double(frac));
DtUTC.Format = 'uuuu-MM-dd''T''HH:mm:ss.SSSSSSSSS''Z'''
More Answers (1)
dpb on 11 Nov 2021
>> t='1294871257.002060945'; % treat long value as string
>> dsec=seconds(str2double(extractBefore(t,'.'))) + ...
seconds(str2double(extractAfter(t,strfind(t,'.')-1))); % combine integer/fractional parts
>> dsec.Format='dd:hh:mm:ss.SSSSSSSSS' % format to show nsec resolution
This is the most straightforward workaround I can think of within the limittions of the (somewhat hampered) durations class which has limited input options for formatting input and the helper functions such as seconds that are only base numeric classes aware.
The datetime class is still pretty young; it has much left to be worked out in order to make it fully functional over niche usage such as yours.
You'll probably have to build a wrapper class of functions to hide all the internal machinations required; the above just illustrates that if you can break the whole number of seconds precision required into pieces that are each within the precision of a double that the duration object itself can deal with them to that precision -- at least storing an input number. I've not tested about rounding when try to do arithmetic with the result.