Lake Simulator

Numerical simulation, using existing hydrodynamic/water quality models, can be an effective way to study ecosystem dynamics while accounting for complex physical and biological interactions. Unfortunately, numerical simulations tend to be very difficult to setup, they take a long time to run, and provide predictions that can be difficult to synthesize and interpret. As a result, this analytical approach typically has been used in engineering fields much more than ecology. To bring the power of numerical simulation to the ecological community, we have developed Lake Simulator.


The GLEON Simulator Web site allows users to submit numerical simulations of lakes to the CDI Condor pool. The user may submit a single simulation or hundreds or even thousands of simulations. Simulator will package each simulation separately, submit to the GLEON Condor pool, then receive and assemble the results for analysis. To date, hundreds of lake simulations have been run using this resource.


With Lake Simulator, we greatly simplify the input requirements of a numerical model and provide a mechanism for defining many model runs within a single spreadsheet. This allows the user to easily test different combinations of parameter values, for example, or changes to external driving variables, as would be done when running scenarios. Lake Simulator then submits a simulation (or a collection of dozens, hundreds, or thousands of simulations) to the GLEON Condor pool, which distributes those simulations among available compute resources. By distributing the collection of simulations, a job that would have taken days or weeks on a single computer can run and return its results in minutes. Lake simulator also retrieves the results of simulations, extracts the data from the results according to simple user setup defined at job submission, and automatically graphs the simulation results on the Web site. To date, hundreds of simulations have been submitted to Lake Simulator.

Condor

Condor is a high throughput computing platform that supports the running of large computational tasks that would take too long to run on a single or small number of computers. It handles the management of available resources, matching waiting jobs to available computers with the correct architecture and available resources, and the transfer of input and result files (http://www.cs.wisc.edu/condor/). Condor is especially well suited to large computation tasks which can easily be parallelized and exported to run on many individual computers.

Condor is used in the GLEON CDI project to support the simulator system, as well as other analyses. The Simulator software submits to a Condor pool made up of computer resources on the University of Wisconsin – Madison campus, as well as computers distributed throughout the GLEON network. This large pool of computers allows hundreds of individual simulations to be run in parallel, greatly reducing the time required to run complex suites of simulations. Such a system is especially important when simulating large numbers of lakes, bootstrapping models, conducting sensitivity analyses, or running many different models in an ensemble modeling approach.