Stella Architect

Stella Architect is the version of isee systems' Stella software for designing and publishing model-based simulations that other people can use.² A model is drawn as a diagram of stocks and flows that can be simulated over time, so that someone can test what-if scenarios before acting.^1,3 isee systems was founded in 1985 by Barry Richmond and is based in Lebanon, New Hampshire.^1,3 In 1989 the System Dynamics Society gave Richmond its Jay Wright Forrester Award for being the first to introduce an icon-based tool for building and simulating models, STELLA.³ Stella Professional and Stella Architect followed in 2015 and 2016.³

Loops That Matter, released in 2020, shows during a run which feedback loops are driving behaviour.^2,3 Causal Lens traces the causes of a variable's behaviour, and Stella Live updates results as settings change.² There are sensitivity runs and a translator that opens Vensim models.² One model can mix system dynamics with discrete events and some agent-based parts.² Assemblies are premade model structures, with AI suggesting formulas and units.² In 2007 isee committed to XMILE, a draft standard for exchanging models between programs, and in 2012 it released its first XMILE-compatible product.³

What sets Architect apart is the interface builder: knobs, sliders, graphs and storytelling screens on top of a model, published to the web, the desktop or mobile devices so others can run it in a browser.² An add-on publishes models to run inside Excel.² The non-academic price is $3,999, with subscriptions of $539 for two months, $1,269 for six months and $1,929 for a year.² There is a free 30-day evaluation licence, and Stella Online, an online model editor, and isee Player are free.^1,2

isee's examples include public policy work on urban planning and natural resource management, and conservation models of eutrophication, salmon fishing and water allocations to towns.² For a group working on a place, the draw is a model of a watershed or a housing market that people in a meeting can change and rerun themselves. Models made in Stella can also be exported as XMILE and run in Python with PySD.⁴