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Connecting to a running simulation

Computer simulations often take weeks or months to complete and it is often necessary to visualize data from the simulation before it has completed in order to diagnose potential problems. Newer versions of VisIt come with a simulation interface library that can be linked into your serial or parallel simulation application in order to provide hooks so VisIt can plot data from your running simulation. When instrumented with the VisIt simulation interface library, your simulation can periodically check for incoming VisIt connections. When VisIt successfully connects to your simulation, all of your simulation variables are avaiable for plotting without having to write plot files to disk. During the time that VisIt is connected, your simulation acts as a VisIt compute engine in addition to its regular responsibilities. You can pause the simulation while using VisIt to interact with the data or you can choose to have the simulation continue and push new data to VisIt for plotting. For more information about instrumenting your simulation code with the VisIt simulation library interface, send e-mail to visit-users@ornl.gov.

VisIt currently treats simulations as though they were ordinary files. When the VisIt simulation interface library is enabled in your application, it writes a special file with a .sim extension to the .visit/simulations directory in your home directory. Each .sim file encodes the time and date it was created into the file name so you can distinguish between multiple simulations that VisIt can potentially open. A .sim file contains information that VisIt needs in order to connect via sockets to your simulation. If you want to connect to a simulation, you must select the .sim files corrsponding to the simulations to which you want to connect and add them to the Selected files list (Figure2-4). Once you've done that, connecting to a simulation is the same as opening any other disk file.