Why am I getting negative seconds when subtracting clock times?

I'm trying to create a function that subtracts the start time from the end time of a trial to calculate the trial duration:

trialstart{n_trial} = clock;
trialend{n_trial} = clock;
trialduration{n_trial} = trialend{n_trial}-trialstart{n_trial};

For many trials the code works fine, with trialduration results like the following:

[0,0,0,0,0,7.3425]

However, I notice that when a trial extends from the end of one clock minute into the start of the next clock minute, the trialduration function returns a positive minutes value and a negative seconds value, like this:

[0,0,0,0,1,-53.4844]

This is, of course, not wrong...but I would much prefer to just see a positive number of seconds each time. Any suggestions would be appreciated. Thanks in advance.

Answer 1

[jonas]

You could use:

tic  %at start of trial
DurationTrial = toc

Or alternatively

StartTrial = datetime('now')
EndTrial = datetime('now')
DurationTrial = EndTrial - StartTrial

Returns duration format

[Steven Lord]

You would probably want to use datetime('now') or just plain datetime instead of datetime('today').

[jonas]

Oh yes, you are right. Ill update, thanks!

[Sarah]

This is perfect, thank you so much Jonas!