Loop

Element used to identify causal loops in System Dynamics models.

Loop is just a graphical identifier, consisting of a label with a brief description of the loop meaning and an arrow showing the loop direction. It does not define the causal loop itself, but only shows information about existing causal dependencies in your stock and flow diagram, i.e. shows how variables affect one another. 

Adding loops, you can help other users of this model to understand influences and causal dependencies that exist in the stock and flow diagram.

Reinforcing and balancing loops

Loops are either reinforcing or balancing.

To determine if a causal loop is reinforcing or balancing, one can start with an assumption, e.g. "VariableN increases" and follow the loop around. 

The loop is:

Or you can use the alternative definition:

There are two loops in the diagram shown in the figure below: one reinforcing and one balancing:


 To add a loop

  1. Drag the Loop  element from the  System Dynamics palette to the graphical diagram of the agent.
  2. Go to the Properties view to set up properties of the loop. 
  3. Set the Direction of this loop - either Clockwise or Counterclockwise
  4. Choose the symbol that you want to be shown for this loop from the Type group of buttons. You can choose B (stands for Balancing), R (Reinforcing), or specify your own text in the edit box to the right. We recommend you to number your loops (R1, B1, R2, etc.) to simplify referencing them by the users of the model.
  5. You can specify a brief description of the loop (usually - two or three words) that will be shown on presentation in the Text property.
  6. Optionally you can type more detailed description of this loop on the Description property page (but it will not be visible on the presentation, users will be able to see it only on this particular property page and in the model documentation).

Properties

Direction – Here you can specify the direction of the loop - whether it is Clockwise or Counterclockwise.

Type – Here you can choose the symbol that will be shown by the loop element. You can choose B (stands for Balancing), R (Reinforcing), or specify your own text in the edit box to the right.

Color – The color of the loop (both the text label and the arrow). By default loops are shown blue. However, you can change the default color to any other you want.

Text – Here you specify a brief description of the loop that will be shown on presentation.


Related topics

 System Dynamics tutorial

 System Dynamics modeling