Simulator Program

The largest program is the simulator. This is written in C++, and works in a similar way to the other two program combined.

Each type of network is implemented as a class. Each class has the following important variables:

• Width and Length specify the size of the network.
• CLengthSqu specifies the characteristic length of the network.
• Sources is an array of voltages at the input nodes. These can be changed dynamically during the simulation to simulate the effect of motion.
• HConnected and VConnected can be used to manually turn on or off resistive fuses.
• LargestChange is used by the simulator to keep track of the largest change in output voltage in the last iteration. When this falls below a threshold, the simulator stops.

There are also a number of important functions for each class:

• InitialiseNodes is used to set the output node voltages equal to the input node voltages, as a neutral starting point for simulation.
• Iterate recursively performs iterations of solving for currents and voltages. The variable Increment controls how much closer to the solution the node voltages move at each step--0.1 means 10% closer, for example.
• PrintNodeTable prints the output nodes on standard output.
• PrintSegmentation prints an ascii art representation of which resistive fuses have tripped.
• PrintPostscript prints a postscript file with the specified name which represents the output nodes, and PrintEdgesPostscript does the same but with dotted lines representing the resistive fuses that have tripped.

The algorithm that Iterate uses to compute the output voltages is simplified based on knowledge of the network. For example, it is not the actual currents that are solved for, but rather the voltage differences across resistive fuses. These are then divided by the characteristic length, which means that only the characteristic length of the network needs to be specified, instead of both the source resistance and the interconnection resistance. The program uses an idealised model of a resistive fuse, and simply uses a if clause which detects if the voltage difference across the resistive fuse is larger than the threshold, and sets the current to zero if it is.

The program has a makefile and is compiled by typing make on the command line. This produces the executable sim. Simply invoking sim on the commmand line produces text output on standard output as well as the same output files that decode produces.