Ground truth is missing and the measurements is wrong.

[kimukook]

You didn't have ground truth of states in your implementation, how could you show that your code really works well with Kalman Filter?
To show that your code actually implements Kalman Filter, your filtered states should have smaller error compared with predicted states. But in your code, only the filtered states are provided.

The measurements here is generated from a parabola -(x**2+2x02). But this is not the actual curve.