Kalman Filter in matlab

Hi everyone! I am having a video and I have to locate the position of ball using Kalman equations. Suppose the initial position(xi,yi)is known. for the first frame current position is (xi,yi).Please guide me what would be the current position(currx,curry;as in the code below)in the next frames.The piece of code is:

R=[0.2845 0.0045;0.0045 0.0455];

Hi=[1 0 0 0;0 1 0 0];

Q=0.01*eye(4);

Pe=100*eye(4);

F=[1 0 0 0;0 1 0 0;0 0 1 0;0 0 0 1];

x=zeros(569,4); 

kfinite=0;

for k=1:nframes

if kfinite==0 % kalman initialization

Au=[xi;yi;0;0];

currx=Au(1);

curry=Au(2);

    else

        u=[x1;y1;0;0];

        Au=F*x(k-1,:)'+u; % Prediction 1st equation

        currx=xi

        curry=yi

end

        vx= currx-Au(1);

        vy=curry-Au(2);

        xactual=[currx;curry;vx;vy];

        xactualnext=F*xactual;

        ydesirednext=Hi*xactualnext;

        pp=F*Pe*F' + Q;   %Prediction 2nd equation

        K=pp*Hi'*inv(Hi*pp*Hi' +R);  %%%correction 3rd equation

        Anu=Au + K*(ydesirednext-Hi*Au);  %%correction 4th equation

        Pe=(eye(4)-K*Hi)*pp;  %%correction 5th equation

        x1=Anu(1);

        x2=Anu(2);

        kfinite=1;

    end

Answer 1

[John Petersen]

You are using +u in the prediction equation but not in the "actual" equation. Could this be your error?