ising_2d_simulation, a C code which carries out a Monte Carlo simulation of a 2D Ising model, using gnuplot to display the initial and final configurations.
A 2D Ising model is defined on an MxN array of cells. Each cell can have a "charge" or "spin" of +1 or -1. A neighborhood of a cell is defined to be itself, and the four immediate neighbors to the north, south, east, and west. A cell may change its charge; the likelihood of doing so depends on whether the charge of the neighbors agrees with the charge of the cell.
This program begins with a random assignment of charges to the cells. It then computes the neighbor agreement at each cell. It then updates the entire configuration in one step, using the neighbor agreement to determine the likelihood of flipping.
Currently, the chance that a cell will "flip" is determined from a table of probabilities based on the number of agreeing neighbors:
ising_2d_simulation m n iterations thresh seedwhere
Note that the user might also want to vary the transition probabilities. This cannot currently be done on the command line, and requires editing the program and recompiling it.
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
ising_2d_simulation is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version.
BROWNIAN_MOTION_SIMULATION, a C code which simulates Brownian motion in an M-dimensional region.
DUEL_SIMULATION, a C code which simulates N repetitions of a duel between two players, each of whom has a known firing accuracy.
FOREST_FIRE_SIMULATION, a C code which simulates the occurrence of fires and regrowth in a forest, displaying the results using X Windows, by Michael Creutz.
gnuplot_test, C codes which illustrate how a program can write data and command files so that gnuplot can create plots of the program results.
HIGH_CARD_SIMULATION, a C code which simulates a situation in which you see the cards in a deck one by one, and must select the one you think is the highest and stop; the program uses GNUPLOT for graphics.
MANDELBROT, a C code which generates an ASCII PPM image of the Mandelbrot set;
POISSON_SIMULATION, a C code which simulates a Poisson process in which events randomly occur with an average waiting time of Lambda.
REACTOR_SIMULATION, a C code which a simple Monte Carlo simulation of the shielding effect of a slab of a certain thickness in front of a neutron source. This program was provided as an example with the book "Numerical Methods and Software."
STRING_SIMULATION, a C code which simulates the behavior of a vibrating string.
THREE_BODY_SIMULATION, a C code which simulates the behavior of three planets, constrained to lie in a plane, and moving under the influence of gravity, by Walter Gander and Jiri Hrebicek.