private void computeCoefficientOfDetermination() {
int numberOfItems = scatterpointsDataset.getSeries(0).getItemCount();
double arithmeticMeanOfX = 0; // arithmetic mean of X
double arithmeticMeanOfY = 0; // arithmetic mean of Y
double varX = 0; // variance of X
double varY = 0; // variance of Y
double coVarXY = 0; // covariance of X and Y;
// compute arithmetic means
for (int i = 0; i < numberOfItems; i++) {
arithmeticMeanOfX += scatterpointsDataset.getXValue(0, i);
arithmeticMeanOfY += scatterpointsDataset.getYValue(0, i);
}
arithmeticMeanOfX /= numberOfItems;
arithmeticMeanOfY /= numberOfItems;
// compute variances and covariance
for (int i = 0; i < numberOfItems; i++) {
varX += Math.pow(scatterpointsDataset.getXValue(0, i) - arithmeticMeanOfX, 2);
varY += Math.pow(scatterpointsDataset.getYValue(0, i) - arithmeticMeanOfY, 2);
coVarXY +=
(scatterpointsDataset.getXValue(0, i) - arithmeticMeanOfX)
* (scatterpointsDataset.getYValue(0, i) - arithmeticMeanOfY);
}
// computation of coefficient of determination
double r2 = Math.pow(coVarXY, 2) / (varX * varY);
r2 = MathUtils.round(r2, Math.pow(10.0, 5));
final double[] coefficients = Regression.getOLSRegression(scatterpointsDataset, 0);
final double intercept = coefficients[0];
final double slope = coefficients[1];
final String linearEquation;
if (intercept >= 0) {
linearEquation = "y = " + (float) slope + "x + " + (float) intercept;
} else {
linearEquation = "y = " + (float) slope + "x - " + Math.abs((float) intercept);
}
TextTitle tt = new TextTitle(linearEquation + "\nR² = " + r2);
tt.setTextAlignment(HorizontalAlignment.RIGHT);
tt.setFont(chart.getLegend().getItemFont());
tt.setBackgroundPaint(new Color(200, 200, 255, 100));
tt.setFrame(new BlockBorder(Color.white));
tt.setPosition(RectangleEdge.BOTTOM);
r2Annotation = new XYTitleAnnotation(0.98, 0.02, tt, RectangleAnchor.BOTTOM_RIGHT);
r2Annotation.setMaxWidth(0.48);
getPlot().addAnnotation(r2Annotation);
}
