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====== Running VisIt ======

There are three versions of VisIt installed on Lengau:
  - Visit-2.10.2 
  - Visit-2.13.3 
  - Visit-3.1.1 


All three versions are available as modules.  Use the command ''module avail 2>&1 | grep VisIt'' to find the module names.   Please refer to the [[https://wci.llnl.gov/simulation/computer-codes/visit/|VisIt web site]] for more information on VisIt.  For interactive graphics, an OpenGL-enabled environment will be required, therefore refer to the page on [[howto:remote_viz|Remote Visualization]] for instructions on setting up a connection to the visualization node, and running VisIt with the VirtualGL wrapper. VisIt is an extremely versatile post-processor, and can be used as the primary visualization tool for a very wide range of applications and file formats. 

===== Running VisIt on a visualization node =====
It is possible to run a VisIt client on your local workstation, with the data and render processing happening on a cluster node.  However, is is easier to use one of the visualization nodes (chpclic1 or chpcviz1) to run the interface.  In order to do this, load the module ''chpc/compmech/VisIt/2.12.3-VNC'', and start VisIt with the command ''vglrun visit''.  This will get you a serial version of VisIt, which is adequate for processing smaller data sets. 

==== VisIt on a viz node with the compute engine on a compute node ====
In order to visualize large data sets effectively, add one or more compute nodes. For VisIt to be able to start the remote compute engine on a compute node, three modules need to be loaded by default, which is most easily achieved by inserting these three lines in your ~/,bashrc file:
<code>
module load gcc/6.1.0
module load chpc/compmech/mpich/3.2/gcc-6.2.0
module load chpc/compmech/mesa/17.0.1
</code>


However, the mesa module will clash with the VNC implementation of VisIt, therefore you will need to unload it in your VNC session before starting VisIt.

Now start VisIt in your VNC-session, as per usual.  To get access to a full compute node, start an interactive PBS session: 
<code> qsub -I -X -l select=1:ncpus=24:mpiprocs=24 -l walltime=4:00:00 -q smp -P MECH1234 </code> 

Note down the hostname of the compute node assigned to you.  In this case, it is cnode0756.

In VisIt, go to the ''Options - Host Profiles'' menu and fill in the necessary details as per this example

{{:howto:visithost.png?nolink |}}


Click Apply, and then set up an appropriate parallel host profile:

{{:howto:visithostprofile.png?nolink |}}


Click Apply and dismiss the form.

Now go to the ''File - Open'' menu:

{{:howto:visitopenfiles.png?nolink |}}

Change the host from localhost to your compute node, and if all goes well, you can select the appropriate data file on the compute node.

{{:howto:visitopenfiles2.png?nolink |}}

You are then given the option of selecting the number of parallel processes you want to use on the compute node:

{{:howto:visitopenfiles3.png?nolink |}}


From here onwards proceed as usual.  Note that you will only get parallel acceleration if your data set is parallel.
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