/** Creates a particles at random locations. */
public void calculate() {
frame.clearDrawables(); // remove old cirlces
int n = control.getInt("number of particles");
double r = control.getDouble("radius");
for (int i = 0; i < n; i++) {
double x = -10 + 20 * Math.random();
double y = -10 + 20 * Math.random();
frame.addDrawable(InteractiveShape.createCircle(x, y, r));
}
}
