mcwitt / ifm

Monte Carlo simulation of Ising ferromagnets using Wolff cluster updates.

Monte Carlo simulation of Ising ferromagnets

ifm is a simple and efficient implementation of the Wolff cluster algorithm (Wolff, 1989) for Monte Carlo simulation of Ising ferromagnets. It is optimized for very large lattices and can handle billions of spins.

Basic usage

Simulation parameters are defined as macro constants to allow for effective compiler optimization. Use the script setup.sh to prepare a build for a given set of parameters. Binaries with different sets of parameters should be built in separate directories.

For example, to build a simulation of a 2-d model on a 64x64 square lattice with periodic boundary conditions:

mkdir -p build/d2-L64
cd build/d2-L64
BC=BC_PERIODIC LT_D=2 LT_LMAX=64 ../../setup.sh
make

The ifm binary takes a single optional argument, which is used to seed the random number generator. Temperatures are read from standard input. Typical usage looks like

./ifm 123 < temps.txt > d2-L64-123.dat

Parameters

The following environment variables are used by setup.sh:

Basic parameters

Parameter	Type	Description
BC	{BC_PERIODIC,BC_FREE}	boundary conditions
LT_D	integer	dimension of lattice
LT_LMAX	integer	linear size of lattice
LOG_TIME_THERM	integer	log time to thermalize
LOG_TIME_MEAS	integer	log time to measure

Advanced parameters (usually don't need adjustment)

Parameter	Type	Description
RNG	[see rng.h.in for values]	type of random number generator to use
UPDATES_PER_STEP	integer	number of cluster updates per unit time
MAX_STACK_SIZE	integer	size of the stack used for cluster updates