# Out of Memory Alerts

Whenever you attempt to do something that requires more RAM than has been allocated to the software, you will receive an alert which states that you are out of memory. When you run out of memory, there is no recourse but to quit the program. You have the option of saving your model under a different name, thus preserving any work that you have done since the last Save command. Below are listed typical causes of this alert, as well as some memory-expanding options.

Causes of Out of Memory Alert:

- Multiple-element arrayed structures. Arrays can use up memory while taking up relatively little diagram structure.

- Too much output in comparative graphs/tables. The output displayed in comparative tables and graphs is stored in RAM. As a result, a multiple-run sensitivity analysis, with several comparative graphs/tables, can quickly consume much of the memory allocated to the software.

- Conveyors with long constant or variable transit times. Conveyors with variable transit times are deceptively simple looking. Beneath the scenes, however, such conveyors require a lot of RAM.

- Long simulations with small DT: Memory requirements for a simulation increase proportionally with the length of the simulation, and inversely with the size of DT. Longer simulations and smaller DTs will require more memory.

- Analyze mode. When this option is turned on in the Run Specs dialog, model output for all model variables is stored in RAM. With various combination of a large model, a long simulation, and a small DT, memory can very quickly be consumed.

- Graphic images: Some graphic images can be exceedingly memory intensive. If you do not have sufficient memory to display a graphic image within your model, the image will not be drawn and the graphics object will provide you with a text message.

- DELAY functions with long delay times.

- DERIVN function with a large number for the order.

- SMTHN functions with a large number for N.

- POISSON or EXPRND functions with a large mean: Because these functions use a recursive technique to calculate the next number in the sequence, large values for the mean can slow the execution of the simulation and can require deceptively large amounts of memory.

Memory-Expanding Options:

- Save your work early and often. In so doing, you will minimize the amount of work you will lose if your machine ever “crashes.”

- On the Mac, adjust the memory partition to accommodate the memory constraints. [Quit out of the software; click once to highlight the ithink or STELLA icon on the desktop; choose Get Info from the File menu of the Finder; increase the Preferred Size to a level appropriate to your model size and available RAM.]

- Periodically clear the data displayed in comparative graphs and/or tables. Choose Restore Graphs and Tables from the Interface or Model menu to clear the data. This will free a corresponding amount of memory in RAM.

- Get more RAM. These days, RAM is perhaps the most cost-efficient computer investment you can make. It’s cheap. It’s readily available. And, it’s easy to install. It’s probably the best way to relax memory constraints.