Stella IPad App Review – Mobile System Dynamics

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As someone who actively uses system dynamics to tackle complex issues for clients using the pricier iThink software from isee systems, I was quite intrigued when isee released a system dynamics app for the iPad

I should note right off that the app as of this review is $40, so pricey by iPad app standards, but for anyone who owns the full desktop software this will seem like a steal. In fact, I believe one of isee’s objectives with the app is to democratize the exploration and use of systems dynamics as a tool for addressing complex problems, and I applaud them for this.

When you first open the app and create a new model, you are provided a clean canvas to work with on which you can tap to add stocks, flows and converters. As you will see in the image below, I have added a stock for “Visitors” and simple flows of “New Visitors” and “Abandoning Visitors”.

As this is isee’s first effort at an iPad app, I was pleased with the ease of adding, moving, resizing and connecting these basic objects.


In addition to the basic stock and flow, it is very simple to add neccessary converters and connectors between all the objects, as the image below shows. For each of the objects, there is a setting section that allows you to change the underlying formulas and constants for the variables as well as basic settings for the variable, such as whether flow is uni or bi directional.


One of the really cool features in this app is the ability to establish graphical input functions. The ability to easily set up non-linear inputs with the ease of drawing the relationship with your figure creates the capacity to quickly experiment with the “shape” of a non-linear input variable. The fact that this is so easy to do makes me more likely to explore these dynamics in models, which I believe helps make me more accurate in my modeling.


Another great feature given the limited canvas space of the iPad is the ability to create multiple “modules”. These modules allow you to set up other related dynamic components that are built on seperate canvases, creating the ability to break a complex model in smaller pieces for development on the iPad.

For each model developed, you also have the ability to customize some basic settings including; start and stop time for the model, the time step and time unit in the model, the simulation speed and the integration model (Euler, RK2, RK4)

Once you have crafted your clever model, the real fun begins with simulation. I was quite please with how simple it was to run a simulation for the model. Simply choose simulate and then run and watch your simulation play out.

One of the great things about simulation, is that it helps enforce to viewers that dynamics play out over time. Too often I run into models that suggest immediate change or impact, but do little to explore the dyamics that take place over time and that the “outcomes” are different at different points in time. The simplest example of this flaw is when startups focus on annual P&L’s that show profitability in Year 1, but do little to assess the dynamic and monthly shifts in profitability, losses and cash flow. Companies may look wonderful when they reach maturity, but most of them fail on the path to maturity.

Once a simulation has been run, it is easy to view the results as graphs for each input, flow and stock. A simple click on the object yields the chart in larger view. You also have the ability to simply “zoom” in on the object to see its outcomes.

In addition to viewing, you can also drag your figure along the chart to see the specific x,y coordinates, which is helpful if you are drilling in on key moments in the simulation.


Finally, once you have created an insightful model that would impress the brightest Systems Design students at MIT, it’s time to share your model. The primary way to share your model is to email it to interested parties as a Stella model.

This sharing capacity is one of the serious limitations of the app to date. I currently use iThink, which is the brother to Stella, and capable of opening the Stella model. I open in iThink and then share the model using iThink as a public simulation.

If you do not own either Stella or iThink, your ability to share the model is limited to taking a picture and sharing as such. In addition, there is no way that I could find to access the actual output behind the graphs without exporting to Stella or iThink.

I understand that it is not likely that they will recreate all this functionality in a $40 iPad app, but given the stated and admirable objective of increasing the understanding and use of system dynamics, I think the software would get far greater adoption if some simple features were put in place to access the output data and to share the map easily as a PDF.

One of my dreams would be if isee could find a way to push these models out as simple “runable” simulations with the ability to control inputs and parameters. As I was writing this review isee released an update to the Stella app that allows you to adjust inputs for the simulation by turning the converters into adjustable dials. This rapid and meaningful update gives me hope that this app will continue to improve.

Regardless, this is now a solid tool in my system dynamics workflow. I have found myself building simple models while on the road or in my free time, and then as approriate moving the models to iThink for further development or refinement.

I am looking forward to seeing where isee goes with this app. If you have tried the app, let me know what you think of it? Do you think we will ever get to a point where we can develop, run and share dynamic system models online without full featured software? Will this lower the barrier to adoption of system dynamics as a thinking tool?

About Brian

Innovation & Strategy Specialist; Focus on Innovation Roadmapping & Business Modeling; Husband, Father, Systems Thinker, Babson MBA, Triathlete. View all posts by Brian →

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