[ewilliams]

Another strong player (especially since a major release 7 recently) is the simulation software Extend. Extend is particularly strong for models in which continuous and discrete concepts must be intertwined (e.g. fluid flows continuously from Tank 1 to Tank 2 until Tank 2 reaches a certain level -- then a valve closes (open versus closed is discrete) and the flow rate drops suddenly and discontinuously to zero. Here is another situation easy to model in Extend and difficult in other packages: a ship enters a dock and 2 cranes begin to unload it. After both have worked for awhile, one breaks down and the other keeps working. A little later, the broken crane is repaired and returns to help the first one. When will the ship be completely unloaded of its cargo?