HomeTroubleshooting@RISK for Excel: SimulationSimulation Crashes with Increased Number of Iterations

4.3. Simulation Crashes with Increased Number of Iterations

Applies to:
@RISK 6.x/7.x

My simulation runs fine with a larger number of iterations, but when I increase the number of iterations to 5,000 (or 10,000, or 1,000, or some larger number) then the simulation crashes.

This sounds like a Multiple CPU problem. To understand it, let's talk a bit about how Multiple CPUs (cores) work in @RISK.

By default, in Simulation Settings » General, Multiple CPU is set to Automatic, meaning that @RISK tries to guess whether a simulation will run faster with multiple CPUs or with one CPU. When you increase the number of iterations, @RISK may change its approach from one CPU to multiple CPUs.

In @RISK 7.0.1 and older, the default was called Enabled instead of Automatic, but it functioned as described above. Starting with @RISK 7.5.0, that behavior was called Autoamatic, and Enabled was given a new meaning.

When a simulation is run in multiple CPUs, @RISK launches an invisible "worker" copy of Excel for each of the extra CPUs. The "master" copy, the one with windows on screen, parcels out iterations to the workers and integrates the results that they pass back. At the end of simulation, the master sends instructions to the workers to shut themselves down, and after they've done it the master creates any graphs and reports and the Excel status line displays Ready.

The two critical points in this process are starting up the extra copies of Excel, and shutting them down. There are Microsoft-standard protocols for both operations, but on some computers they don't work, or don't work reliably. Since @RISK needs to wait for the requested CPUs to open or to close, there's a bottleneck, and it may look like Excel has crashed.

If a simulation crashes with multiple CPU but runs to completion with a single CPU, you've probably got a problem with starting up the worker Excels or shutting them down.

If Excel seems to freeze when initialization is 100% complete, please see Progress Window Freezes at "Initializing ... 100%".

If this happens when simulation is 100% complete, then you can kill the "zombie" workers in Task Manager without losing any of your results. Press Ctrl+Shift+Esc to open Task Manager. On the Details tab (Processes tab in Windows 7 and earlier), click the column heading Name or Image name to alphabetize the running programs, then locate the copies of Excel.exe. One of them, the master, will have significantly higher memory use than the others. Kill the others, the workers, using End Task. When the last worker is shut down, the master will begin cleaning up after the simulation, and you should be able to view your results.

Try a simulation with the same number of iterations, but with Multiple CPU set to Disabled. If it finishes in acceptable time, you have a simple workaround for the problem. If it takes too long to simulate with one CPU, or if you just want the problem fixed, please contact Palisade Technical Support and provide your software serial number with a problem description.

Last edited: 2018-03-06

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