April 6, 2012

It’s election year in the United States, and in today’s exercise we have an election simulation. It comes to us from chapter “Five Easy Pieces” in A. K. Dewdney’s book The Armchair Universe, which is a compilation of some of Dewdney’s “Computer Recreations” columns in Scientific American. Dewdney calls his simulation voters.

The simulation is simple. A rectangular x-by-y grid contains cells that represent voters. Each cell has eight horizontally, vertically or diagonally adjacent neighbors, with the grid wrapping around on all sides to form a torus. Each cell can contain one of two values, which we call 0 and 1, not necessarily in order, instead of Democrat or Republican. At each time step, one cell, chosen at random, changes its allegiance to that of one of its eight neighbors, chosen at random; in some cases that random choice leaves the allegiance unchanged.

The current state of the simulation is displayed on the screen, with easily distinguishable symbols for 0 and 1. The simulation continues until it reaches a steady state — totalitarianism — in which all cells have the same value. It is mesmerizing to watch the screen as voting blocks form and changing allegiances sweep across the grid.

Your task is to write a program that displays the simulation described above. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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