prevent rounding in datevec

Hi there,

I'm currently trying to concatenate some time series data and I need to add the duration/time lapsed from the end of one block to the other. The time lapsed is written to a .txt like so '_00:17:27.450644'.

I have been trying to extract the hour, minute, seconds and milliseconds values to add these to the next trial which appears as '_00:00:00.049061'.

What I have been using is the following as this at least gives me three decimals of milliseconds

addtime = datestr(strrep(Timelapsed(2801), '_', ''), 'HH:MM:SS.FFF');
[~, ~, ~, H,MN,S] = datevec(strrep(Timelapsed(2801), '_', ''), 'HH:MM:SS.FFF')

But even after using format longE I get

        H =
             0
        MN =
            17
        S =
             2.745000000000000e+01

When really I need to get the exact value 27.450644.

I would like to be able to add these values (H,MN,S) to each value in the remaining trials, like so.

newtime = datestr(strrep(ROMOD22{2802, 5}, '_', ''), 'HH:MM:SS.FFF'); % for example '_00:00:00.049061'
    [~, ~, ~, H1,MN1,S1] = datevec(newtime, 'HH:MM:SS.FFF');
    newH = H+H1;
    newMN = MN+MN1;
    newS = S+S1;
    str = ['_0' num2str(newH) ':' num2str(newMN) ':' num2str(newS)];
    ROMOD22{2802, 5} = cellstr(str);

But then of course my result is rounded

'_00:17:27.499'

As really my result should be 00:17:27.499705. Although it doesn't seem like much I'm working with some extremely time sensitive data and need those extra milliseconds. I tried using datenum and datetime but datevec seems to be the only one that gives me milliseconds. If anyone has any idea on how to prevent the rounding I would very much appreciate it.

Kindly, Alie

Answer 1

[Walter Roberson]

This is simply not possible with datenum.

>> eps(now)*24*60*60
ans =
      1.00582838058472e-05

This establishes that the time resolution is about 1E-5 seconds, which is about 10 microseconds, but you need time resolution down to 1 microsecond.

>> T = datetime(); T.Format = 'HH:mm:ss.SSSSSS'
T = 
  datetime
   22:43:56.457037