MATLAB: Confusing problem about duration data

MATLAB

Hi,
I'm having a very confusing issue when I'm operating with duration data. I'm new to this data type. Here I debugged my code and simplify my question as an example. Please can someone point out the root reason of why this is not working. Basically, I first define a duration x and with this x, I want to create a new x1 with a random duration, like in the example. I describe my confusion as below. Can anyone help me out? I know it might be the problem of using rand but why?
x = duration(8,0,47);
>> x1 = x + rand*duration(0,0,10);
>> x1
x1 =
duration
08:00:54
However, I realize though x1 is of type of duration, it does not equal to the duration 08:00:54.
>> x1 == duration(8,0,54)
ans =
logical
0
Nevertheless, if I define a new x2 in a similar way, it works.
>> x2 = x + duration(0,0,7);
>> x2
x2 =
duration
08:00:54
>> x2 == duration(8,0,54)
ans =
logical
1
And x1 apparently doesn't equal to x2.
>> x1 == x2
ans =
logical
0

Best Answer

  • rand() produces a 53 bit random number in the range 0 to 1, effectively randi([1 2^53-1],1,1) / 2^53
    When you multiply this by 10 seconds, it is very unlikely to happen to result in an exact multiple of 1 second.
    This is not obvious because the default output for duration does not display fractions of a second.
    x1.Format = 'hh:mm:ss.SSSSSSSSS';