Created
January 12, 2012 13:49
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1D Ising model with periodic boundary conditions on the BeagleBone's LEDs
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var bb = require('./bonescript'); | |
leds = [bone.USR0, bone.USR1, bone.USR2, bone.USR3]; | |
stepDuration = 200; | |
arrayLength = 4; | |
coupling = 0.5; | |
temperature = 1.0; | |
setup = function() { | |
for(i = 0; i < arrayLength; i++) { | |
pinMode(leds[i], OUTPUT); | |
digitalWrite(leds[i], HIGH); | |
console.log("LED" + i + " is in output mode."); | |
} | |
}; | |
isingStep = function(isingArray, coupling, temperature) { | |
var picked = Math.round(Math.random()*isingArray.length); | |
var pickedNext = picked+1; | |
// implement periodic boundary conditions | |
if(pickedNext >= isingArray.length) { | |
picked = 3; | |
pickedNext = 0; | |
} | |
var energy = coupling*isingArray[picked]*isingArray[pickedNext]; | |
var energyNew = (-1)*coupling*isingArray[picked]*isingArray[pickedNext]; | |
console.log("E=", energy, " E_new=", energyNew); | |
if(energyNew <= energy) { | |
isingArray[picked] = isingArray[picked]*(-1); | |
} else { | |
prob = Math.exp(-Math.abs(energy-energyNew)); | |
console.log("exp(-\beta ∂E)=" + prob); | |
if(Math.random() >= prob) { | |
isingArray[picked] = isingArray[picked]*(-1); | |
} | |
} | |
return isingArray; | |
}; | |
spinToLED = function(index, state) { | |
if(state == 1) { | |
digitalWrite(leds[index], HIGH); | |
} if(state == -1) { | |
digitalWrite(leds[index], LOW); | |
} | |
}; | |
isingRun = function(arraySize, duration, coupling, temperature) { | |
arr = []; | |
for(i = 0; i<arraySize; i++) { | |
arr[i] = Math.round(Math.random()); | |
if(arr[i] === 0) { | |
arr[i] = -1; | |
} | |
spinToLED(i, arr[i]); | |
} | |
console.log("initial config:", arr); | |
while(true) { | |
arr = isingStep(arr, coupling, temperature); | |
console.log(arr); | |
for(i = 0; i < arraySize; i++) { | |
spinToLED(i, arr[i]); | |
delay(duration); | |
} | |
} | |
}; | |
setup(); | |
isingRun(arrayLength, stepDuration, coupling, temperature); |
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