====== Parallel Environment ======

==== Multiple slots in a single node ====

If we want to run a job that uses multiple CPU's, we have to reserve as many slots as CPU's in the queue. To do that, we need to use the SMP environment:

<code>
 qsub -pe smp N
</code>

Where N is the number of slots/CPU's required. Please note that all slots will be reserved in the same node, and if no node has that amount of available slots, the job will wait until that condition is met.

==== Multiple slots across nodes ====

The cluster has a module that sets a parallel environment to run across different nodes. In order to do that, please refer to the OpenMPI documentation to code your program accordingly.

To load the module, simply type:

<code>
module load openmpi
</code>

Now, when we submit a job that will require more than one CPU/slot, either with qsub or qlogin, we can add the following parameter:

<code>
qsub -pe openmpi N ...
</code>

Where N is the number of CPU/slots we would like to use for that job. The cluster will assign N slots to run. You can combine the -l hostname=HNAME parameter to ensure that those slots will be used on a single node if you want. Otherwise, openmpi will distribute the reserved slots across all nodes.