When building a model, you frequently want to compare and contrast different assumptions or cases that the model might be using or exploring. For instance, in financial modelling, interest rates or budget allocations might have significant effects on a model, and be useful to view side-by-side. Silico supports this with the scenarios feature.
An Example Model
For exploring this feature, let's consider a model of interest payments into a bank account. This can be represented with the following model, where an annual interest rate is paid monthly (slightly simplified from the reality of interest calculations):
Using this we can now consider changing parameters or model assumptions, using scenarios.
Adding a Scenario
Scenarios are managed from within the left sidebar, in a collapsible section. By default, every model has a single scenario, called 'Base Case', which represents the model as built. Note that for multi-model projects, scenarios are specific to each model.
Adding a scenario can be done through the + button, and scenario names and colours can be changed by using the triple-dot menu button.
Configuring a Scenario
To configure a scenario, you first make it the active scenario by clicking on the name of the scenario in the sidebar. When in a scenario other than the base case, you cannot edit the structure of the model, and can only edit fields of elements supported by scenarios. Currently this is limited to the formulae and actual data of Variables, Stocks and Flows.
With our New Scenario active, we can click on Interest Rate and change it up to 8% by editing the formula to 0.08:
There's a few visual markers here that are useful to explain:
- The top left of the modelling area will note which scenario you are viewing.
- Elements with scenario configurations to formulae or data will be highlighted with a blue halo.
- Element charts will show lines for all visible scenarios, with the colour of the scenario.
- The value shown on elements will be for the active scenario (and coloured appropriately).
Note that while we just changed a number here, you can change formulae completely per scenario. You can also change the actual data in an element.
Once you have some scenarios configured, you can easily toggle scenarios on/off using the visibility eye buttons within the scenarios sidebar section. Whether a scenario is visible follows these simple rules:
- Scenarios are toggled to be visible if the eye button is active.
- The active scenario is always visible, regardless of their toggled visibility.
- You can have unlimited scenarios visible at once, and scenario visibility is saved with your project.