1D Ising model with periodic boundary conditions on the BeagleBone's LEDs

IsingModel.js

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);