Who can help me explain this?

[yiyon...@gmail.com]

Deal All,

When I run AMPL using solver CPLEX to solve a layout problem. The computing time sometimes took extremely long but sometimes very short for the same code. I did not know why.
Please see the attached picture. The computing time suddenly jumped from 209s to 14650s, and finally it used more than 30,000 seconds to finish the computing. But after I ran it once again, it used only a few hundreds seconds.
While the results are completely the same. I did not know why, this happened already for several times in my past computings.
Is there anybody knows how to avoid this long time computing?

Thanks a lot.

Yiyong

[Robert Fourer]

The "elapsed time" -- also called the "wall clock" time -- is the amount of time you have waited since the CPLEX run began. The most common cause of a big jump in elapsed time, such as you are seeing, is that you put the computer into "sleep" mode during the CPLEX run, and then wake it up much later. However the elapsed time can also be unreliable if there are other programs running on your computer that are sometimes using a lot of resources and slowing it down. Notice that the number of "ticks", which measure CPLEX work independently of what else is happening with the processor, is increasing very steadily unlike the elapsed time.

To avoid jumps in elapsed time, be sure that CPLEX is not interrupted or slowed by other processes.

Bob Fourer
am...@googlegroups.com

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