Learning Forum

[Mehdi Saloo]

Hello Reno,

 

Thanks so much for your swift response.

I need, therefore, always set ncpu= to a negative number of cores (e.g. ncpu=-4) and run double precision in order to get consistent results.

I wanted to ask you one more technical question regarding maintaining consistency. I have read LS-Run User's Guide and found the following relevant information.

“When you are using shared memory parallel processing, the calculations may be executed in different order, depending on CPU availability and the workload on each CPU. Because of this, you may see slight differences in the results when you run the same job multiple times. To avoid these differences, you can specify the number of CPUs as a negative number to maintain consistency. Maintaining consistency can result in an increase of up to 15% in CPU time.”

As far as I understand, when I specify to use multiple cores (e.g. ncpu=4), I am running using parallel processing (i.e. multiple cores), thus getting inconsistent results is probable. I set the number of cores to 1 in LS-DYNA (ncpu=1) to see if repeated runs then produce the same results. In that case, I get inconsistent results, however, I am not running using parallel processing! (when I set  ncpu=-1, I get consistent results.)

I would appreciate it if you could give me some advice.

Thanks in advance.

Regards,

Mehdi