/**
* Compute the centroids of all the clusters.
*
* @param ids Array of cluster numbers which this call will fill in, defining which cluster each
* point belongs to. The caller must leave the data here intact between iterations.
* @param means Array of x,y values in which we will place the centroids of the clusters.
* @return true iff none of the means moved by a significant amount.
*/
private boolean computeCentroids(int[] ids, double[][] means) {
boolean dirty = false;
for (int c = 0; c < numClusters; ++c) {
// Compute the weighted sum of the data points.
double tx = 0.0, ty = 0.0, tot = 0.0;
for (int p = 0; p < numPoints; ++p) {
Point point = dataPoints[p];
double str = Math.pow(clusterStrengths[p][c], M);
tx += point.getX() * str;
ty += point.getY() * str;
tot += str;
}
// Calculate the mean, and see if it's different from
// the previous one.
final double nx = tx / tot;
final double ny = ty / tot;
if (!MathTools.eq(means[c][0], nx) || !MathTools.eq(means[c][1], ny)) {
means[c][0] = nx;
means[c][1] = ny;
dirty = true;
}
}
return !dirty;
}
/** Computes the absolute squared Cartesian distance between two points. */
private static final double computeDistanceSquared(Point a, double[] b) {
final double dx = a.getX() - b[0];
final double dy = a.getY() - b[1];
return dx * dx + dy * dy;
}