The user should be aware of certain limitations that may make it difficult or impossible to use ModelMuse in certain circumstances. ModelMuse can use large amounts of memory—often more memory than is required by the modeling program to execute the model after the model input files are created. For some large models, the amount of memory required may be more than the computer has available; ModelMuse will fail if it runs out of memory. In addition, the 32-bit verion of ModelMuse is not able to use more than three gigabytes of memory; if more memory than that is required, ModelMuse will fail.
To conserve memory, ModelMuse stores some data in temporary files. For large models, these files can be large. If the computer runs out of disk space on the drive containing the temporary files, ModelMuse will fail. When ModelMuse closes normally, the temporary files will be deleted. However, if ModelMuse closes abnormally, such as by having its process aborted in the Windows Task Manager, the temporary files will be left on the disk. When starting, ModelMuse will check for such orphaned files and will delete any it finds. The location of the temporary files will depend on the operating system used and how the operating system is set up. On Windows XP using the default configuration, the temporary files will be in a hidden directory named C:\Documents and Settings\<user name>\Local Settings\Temp\ModelMuse where "<user name>" is the name under which the user is logged into the computer.
When working with large models, it may be necessary to use a computer with a large amount of memory and a large amount of free disk space on the drive in which temporary files are stored. As an experiment to see how much memory and disk space would be required for a large MODFLOW model, such a model was created in ModelMuse. The model had 3.36 x 106 cells (1,400 columns, 800 rows, 3 layers), and a single stress period. The CHD, WEL, RCH and EVT packages were active in this model. The maximum memory in use while the MODFLOW input files were exported was 1.2 GB. The temporary files created while the input files were exported totaled 55 MB. The time required to export all the input files was 21 minutes (processor speed 2.79 GHz, memory 2 GB).
Some operations can be time-consuming for large models. For example, drawing objects in the 3-D-view or drawing the cross sections of objects in a 2-D view other than the one in which the objects were originally drawn can be time-consuming for large models. For that reason, both these operations are turned off when the number of cells or elements in the grid exceeds 100,000. The user can turn them back on again by clicking the Show 3-D objects button 
or selecting View|Show 3-D Objects. The grid lines can be drawn in 2-D relatively quickly even in large models, but there may be so many of them that viewing the objects becomes difficult. The Show 2-D gridlines button 
or View|Show 2-D Grid menu item can be used to display or hide the grid lines in the model.
ModelMuse may not support all the options available for a model. To use unsupported options, the user may need to create additional input files or manually modify input files created by ModelMuse. (Manually created, additional MODFLOW input files can be included in the MODFLOW name file using the Model|MODFLOW Name File... menu item.)
