double[] y = pb.getInitialState();
for (int i = 0; i < 100; ++i) {
y = integ.singleStep(pb, t, y, t + h);
t += h;
}
double[] yth = pb.computeTheoreticalState(t);
double dx = y[0] - yth[0];
double dy = y[1] - yth[1];
double error = dx * dx + dy * dy;
Assert.assertEquals(0.0, error, 1.0e-11);
}