This is due to Matlab itself. If I recall correctly, Matlab uses some sort of 
just-in-time compiler to process the M-files the first time it runs them. After 
that, unless the code changes, it uses the pre-compiled code, and can skip the 
compilation step, making it much faster for future runs. This is particularly 
noticeable when loading extremely large case files.

So, the 2nd and following runs are a more accurate representation of the 
performance.

-- 
Ray Zimmerman
Senior Research Associate
B30 Warren Hall, Cornell University, Ithaca, NY 14853
phone: (607) 255-9645





On Sep 19, 2013, at 2:46 PM, Home Lin <[email protected]> wrote:

> Dear Dr. Zimmerman and Matpower users, 
> 
> I have a question about the running time of runpf and runopf. Say I start 
> matlab and then runopf(case30)  or runpf(case30) continuously for 3 times and 
> their computation time is t1, t2, t3
> I find that t1 is significantly larger than t2, t3, while t2 is similar to 
> t3. 
> 
> Similar thing happens to larger cases, such as case300, case3120sp. 
> 
> Is it because of matlab itself? Does anyone know what is the reason? and 
> which running time correctly refelect the performance of the solver. 
> 
> 
> Thanks,
> Best Regards,
> Lin 



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