QA: How should the numCoresToUse argument in rxOptions be used?

The numCoresToUse parameter in rxOptions allows users to take advantage of multiple cores on their system. The syntax is very simple. If your computer is outfitted with 4 cores, and you want to take advantage of the computational power of all 4 cores, type at the Rconsole: 

> rxOptions(numCoresToUse = 4) 
or 
> rxOptions(numCoresToUse = -1) 

This is only useful is when hyperthreading is turned on on your machine. Because hyperthreading can slow down numerical computations, we recommend setting 'numCorestoUse' to equal the number of actual cores on the computer to avoid this. 
First determine if hyperthreading is turned on. In the Windows Task Manager on the Performance page, there is a separate graph of CPU Usage History for every core the operating system detects. When hyperthreading is turned on, there will be twice as many of these as there are cores.
Users who do not wish to set numCoresToUse using rxOptions can also turn off hyperthreading, but we don't recommend doing this without the assistance of an IT professional.