Simulation models may include a model of a space that is inhabitated by objects. One particular type of a space model is the two-dimensional discrete Euclidean space, called grid space. Due to their simplicity, simulation models based on a grid space have become popular in social science simulation. The wide adoption of the simulation framework NetLogo in social science simulation has contributed to the popularity of grid space models with fixed-increment time progression.
These models may still be considered DES models, even if they do not model any explicit events because their time steps may be viewed as implicit time events, similar to other periodic time events, like "every second", "each Monday", "at end of business week". Time events are a special category of events.
Whenever a grid space model does neither model objects nor events, but only grid cell states and grid cell state changes based on the states of neighbor cells, it may be considered a Cellular Automata model.
Examples of Grid Space Simulation Models with Fixed-Increment Time Progression
- Game of Life: In this famous Cellular Automata model, grid cells may become alive or die depending on their neighborhood: (1) a living cell dies if it has less than 2 or more than 3 living neighbours; (2) a dead cell becomes alive if it has exactly three living neighbours. The Simurena implementation is using an integer grid as the space model such that the integer value of 0 (zero) represents a dead cell and a value of 1 represents a living cell. The model does neither define any object type nor any event type.
- Schelling Segregation Model: A residential area is populated by residents belonging to some group; periodically, all residents check if they are content with their neighborhood, based on their degree of tolerating neighbors of a different group; if they are not, they move to a location where they are content, or leave the area if they don't find such a location.