question on elapsed time
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I am working a problem that require to understand why each operation takes different time. So, I have a
A = randn(100,100);
b = randn(100,1);
tic; x = A\b; toc;
this operation takes about 0.002s
then I do
tic; x= A\b; toc;
MatLab takes slightly shorter times to do the calculation.
As I repeat for a few times, I keep getting two slightly different time. I don't understand why.
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Answers (2)
Star Strider
on 23 Nov 2016
You are getting slightly different times because life is inherently stochastic.
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Walter Roberson
on 23 Nov 2016
- You wiggled the mouse more and that took up some of the computer's attention
- MATLAB does not invoke its garbage collection every time it does an operation, and the amount of time it takes to collect garbage is not constant
- Your anti-virus kicked in for some reason
- Your firewall spent a bit of time disregarding some attack packets from outside
- Some background operation resulted in the data being moved out of the Level 1 cache of your CPU
- Your operating system decided to schedule the work for a different processor and spent a moment moving the process
- Your memory system spent a few jiffy fixing a single bit error
- Your music player decided it was time to check with the mothership to see if a new version of itself was available
- Sunspots
- Because the wise and powerful and rich and wise weasel wished it so
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