Why is tic/toc not reporting the correct elapsed time?

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Ewen Chan
Ewen Chan 2019-8-13
评论： Ewen Chan 2019-8-13
I'm trying to time how long it takes for my program to run and tic/toc is reporting an elapsed time of 150 seconds, but when I time it with a stopwatch, it actually takes 3 hours and 24 minutes for my program to run.
Why is there such a significant discrepancy?
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Walter Roberson
Walter Roberson 2019-8-13
Are you saving the result of tic() into a variable and toc() against the variable? If not then you might have another tic() call that is interfering: toc() reports relative to the most recent tic() that had no output.
Ewen Chan
Ewen Chan 2019-8-13
To be honest, I'm not really sure. I have just been reassigned, so the code is new to me.
What I'm doing is I've wrapped the execution command with tic/toc.
The code times itself and generates a summary automatically for the actual runtimes, but I'm still not sure about the finer workings of it as it is a very complicated multi-system code. There's a LOT to it.

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回答（1 个）

Bruno Luong
Bruno Luong 2019-8-13
编辑：Bruno Luong 2019-8-13
I never have problem with tic/toc. I believe it inquires CPU frequency/counter or clock and derive time from it. It's very direct and simple.
If you get some strange result, then as Walter said something must trigger a later tic when you are not expected.
It might be also safter using tic/toc with timerVal
t0 = tic();
...
dt = toc(t0)
if you are not sure about what happens during "..."
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Ewen Chan
Ewen Chan 2019-8-13
I'll try this today and hopefully, it'll produce a result that's more in line with the internal timers that have been built into the code/program itself.
Thank you.

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