Tic, Toc Behavior

Hi,

I'm curious about the behaviour of Tic-Toc.

Tic-Toc excutes faster in a loop than outside a loop.

Does anyone know exactly why? Some sort of JIT compiliation issue?

Loop Version

TicTocLoop = 0;
for i =1:1:1
    tic;
    TicTocLoop(i) = toc;
end
TicTocLoop

TicTocLoop = 4.8400e-05

Non-Loop Version

TicTocValue = 0;
tic;
TicTocValue = toc;
TicTocValue

TicTocValue = 0.0011

My setup is

MATLAB 2020b

Windows 10

Using Live Script

Thanks for any help

Regards

Cillian

Answer 1

[Fangjun Jiang]

for the sake of fair comparison, the code below should give you reasonable results

%%
TicTocLoop=0;
TicTocValue=0;

for i =1:1:1
    tic;
    TicTocLoop = toc
end
tic;
TicTocValue=toc

TicTocLoop =
   2.7100e-05
TicTocValue =
   1.2300e-05
TicTocLoop =
   2.4100e-05
TicTocValue =
   1.3000e-05
TicTocLoop =
   2.4400e-05
TicTocValue =
   1.3300e-05

[Cillian Hayde]

Hey Fangjun Jiang,

It appears your answer has helped me. It appears to be a live editor issue.

To my eye, tic-toc in a loop is the same for both the m-file and the mlx-file.

The non-looped version is the fastest in the m-file and slowest in the mlx-file.

I personally have no notion why this is, but I will just note it!

Thanks for that!

Regards

Cillian

Answer 2

[John D'Errico]

Using tic and toc to masure any time is a bad idea.

Using tic and toc to masure any time is a bad idea.

Using tic and toc to masure any time is a bad idea.

There, I've said it three times, so it must be true.

Use better tools, best, use timeit. Also you can use the profiler tool, although profiled code will run more slowly, since MATLAB needs to maintian statistics on everything.

[Rik]

Not bad, just often misused. tic and toc should be reserved for situations where you don't care about precision beyond (let's grab a random number) 0.1 second. Actual profiling should be done with the profiler, timing should be done with timeit, and counting seconds can be done with tic. toc.

It is almost as if these names were not chosen randomly (even if tictoc predates the other two).

[John D'Errico]

True about the misused statement. :)

And at times, I use tic and toc myself. But I only ever do that if I warm up the functions in advance, and only for cases when the multiple runs that timeit will perform would be way to time intensive.