/**
* Computes and plots correlation functions
*
* @param tauMax is the maximum time for correlation functions
*/
public void computeCorrelation(int tauMax) {
plotFrame.clearData();
double energyAccumulator = 0, magnetizationAccumulator = 0;
double energySquaredAccumulator = 0, magnetizationSquaredAccumulator = 0;
for (int t = 0; t < numberOfPoints; t++) {
energyAccumulator += energy[t];
magnetizationAccumulator += magnetization[t];
energySquaredAccumulator += energy[t] * energy[t];
magnetizationSquaredAccumulator += magnetization[t] * magnetization[t];
}
double averageEnergySquared = Math.pow(energyAccumulator / numberOfPoints, 2);
double averageMagnetizationSquared = Math.pow(magnetizationAccumulator / numberOfPoints, 2);
// compute normalization factors
double normE = (energySquaredAccumulator / numberOfPoints) - averageEnergySquared;
double normM = (magnetizationSquaredAccumulator / numberOfPoints) - averageMagnetizationSquared;
for (int tau = 1; tau <= tauMax; tau++) {
double c_MAccumulator = 0;
double c_EAccumulator = 0;
int counter = 0;
for (int t = 0; t < numberOfPoints - tau; t++) {
c_MAccumulator += magnetization[t] * magnetization[t + tau];
c_EAccumulator += energy[t] * energy[t + tau];
counter++;
}
// correlation function defined so that c(0) = 1 and c(infinity) -> 0
plotFrame.append(0, tau, ((c_MAccumulator / counter) - averageMagnetizationSquared) / normM);
plotFrame.append(1, tau, ((c_EAccumulator / counter) - averageEnergySquared) / normE);
}
plotFrame.setVisible(true);
}
public void readXMLData() {
energy = new double[0];
magnetization = new double[0];
numberOfPoints = 0;
String filename = "ising_data.xml";
JFileChooser chooser = OSPFrame.getChooser();
int result = chooser.showOpenDialog(null);
if (result == JFileChooser.APPROVE_OPTION) {
filename = chooser.getSelectedFile().getAbsolutePath();
} else {
return;
}
XMLControlElement xmlControl = new XMLControlElement(filename);
if (xmlControl.failedToRead()) {
control.println("failed to read: " + filename);
} else {
// gets the datasets in the xml file
Iterator it = xmlControl.getObjects(Dataset.class, false).iterator();
while (it.hasNext()) {
Dataset dataset = (Dataset) it.next();
if (dataset.getName().equals("magnetization")) {
magnetization = dataset.getYPoints();
}
if (dataset.getName().equals("energy")) {
energy = dataset.getYPoints();
}
}
numberOfPoints = magnetization.length;
control.println("Reading: " + filename);
control.println("Number of points = " + numberOfPoints);
}
calculate();
plotFrame.repaint();
}
