Applies to:
@RISK 5.x and Up

 

“Out of Memory” Errors in @RISK and How to Improve Performance

 

Background:
Windows uses disk space dynamically as virtual memory (paging file). Many applications, including @RISK, write temporary files to your hard drive during simulations. @RISK stores all simulation data in a temporary file used for reports.

Causes of “Out of Memory” Errors:

• Actual memory shortage or insufficient disk space.

• Error may occur before disk space is fully used.

• Opening a Simulation Data window after a large simulation or performing resource-heavy actions.

Speeding Up Simulations:

1. Collecting Input Distributions

• By default, @RISK collects all inputs. Limit this in Simulation Settings → Sampling → Collect Distribution Samples by selecting Inputs Marked With Collect.

• Only collected inputs appear in tornado and sensitivity graphs. Run a pilot simulation to identify influential inputs before limiting collection.

2. Outputs and Statistic Functions

• @RISK stores every output value at each iteration. Remove unnecessary RiskOutput functions or outputs via the Model Window to reduce memory use.

• Statistic functions like RiskMean or RiskPercentile store additional values if referencing cells not marked for collection. Remove unneeded statistic functions.

3. Number of Iterations

• Use convergence testing to limit iterations.

• Run a pilot simulation to estimate iterations needed; use that number or slightly more for the final run.

4. Number of Simulations

• Follow guidance in Iterations versus Simulations for recommended settings.

 

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