When working with models, it can be convenient to organize parameter values into files, often spreadsheets, in order to easily switch between sets of assumptions.
Values can be imported directly into the model, replacing the equations for the imported variables (see Setting Up Import Links for details). In this case, the model equations can be updated when the input information changes, and the saved model contains everything in the data sources that it will use.
Only constants and graphicals can be directly imported. The import process replaces one number with another number, or one series of y values with another series. If an equation is not a number, any values found for it in the import sources will be ignored.
Import control sheets can be used to override model equations. Rather than replacing the equation, the values from the sheets are stored temporarily and used in place of the equations whenever the model is run.
For constants and graphicals, the effect is the same as a direct import, but the equation or specified graphical isn't changed. Disconnecting the import control sheet then has the effect of returning values back to those specified in the equations.
For variables that aren't constant, you can replace the equation for that variable with a constant value, thus breaking connections between inputs and outputs as defined by the model structure. This allows substantial flexibility to turn off portions of model structure. This is true even for graphicals, which can have the value of their result specified directly rather than using the y values of the graphical function.
Imported controls are set up in the Import Control Sheets tab of the panel for the model settings. They override the values of model equations, and may in turn be overridden by interactive changes on either the model or the interface.
When you're working inside of Stella, the import control sheets are read each time the model is simulated. This means that if you send someone a model that uses import control sheets, but don't send them the files for those import control sheets, they'll get different results.
When you publish a model interface, the values from the import control sheets are published along with the interface. The import control sheets are never referenced again after the interface has been published, but the results will be the same as in Stella at the time you published.
You can change values for variables interactively. When working with the model, this is done by adjusting knobs (Stella Live™) or by using the Parameter Control Panel . When working on the interface, values are changed by user entries into any of the input devices (sliders, numerical inputs, and so on) or directly, using a button action. Independent of the source of such interactive changes, they're all stored together. This means that if you're using Stella Architect and drag a slider on the interface, then look at the model, the same value will be displayed for that variable in the diagram.
Interactive changes persist until they're reset using Reset Inputs (as an action on an interface or a menu command on the model) or restore all devices. When you save the model, the values are saved and will persist when you reopen the model (a list of changed values is displayed when the model is open). When you publish a model, the changed values persist on the published model.