Problem with unscented kalman filter

Hi everybody!

I'm trying to implement in matlab a simple unscented or alternatively extended Kalman Filter. At the moment i'd like just to observ a simple pendulum.

So I create a pendulum function and integrate it in 10 seconds with some Initial Conditions:

% pendulum state equation
function dxdt = pendulum(~, x)
    g = 9.81;
    l = 2;
    dxdt = [x(2); -g/l*sin(x(1))]; % state equation
end

% integration function
function [t, x, xdot] = ode

    tspan = [0:0.01:10];
    IC = [pi/4,0];
    
    [t,stat] = ode45(@pendulum, tspan, IC);
    x = stat(:, 1);
    xdot = stat(:, 2);
    
end

[time, x1, x2] = ode; % generating the results

No troubles so far

Then I create an extended Kalman Filter object, a measurment function where I suppose to measure angle Theta and some sensor readings

R = 0.1; % measurment covariance
 
 for i = 1:length(x1)
     y(i) = x1(i) + randn(1)*sqrt(R); %                      sensor readings
 end
 
 
 IC = [pi/4; 0];
UKF_pendulum = unscentedKalmanFilter(@pendulum,@MeasurementFcn,IC);    % UKF object
UKF_pendulum.ProcessNoise = 0.01;
UKF_pendulum.MeasurementNoise = R;

residBuf = [];
xcorBuf = [];
xpredBuf = [];

for i = 1:size(y,2)
    [Residual,ResidualCovariance] = residual(UKF_pendulum,y(i));
    [CorrectedState,CorrectedStateCovariance] = correct(UKF_pendulum,y(i));
    [PredictedState,PredictedStateCovariance] = predict(UKF_pendulum);
    
     residBuf(i,:) = Residual;
     xcorBuf(i,:) = CorrectedState';
     xpredBuf(i,:) = PredictedState';
end

The rest is kept the same with respect to the Van Der Pol oscillator example at this link: https://it.mathworks.com/help/control/ref/predict_method_state_estimation.html

Unfortunately when I try to run i get this message:

Which optional input am I supposed to give to the predict command? I tried with some variables but none of them worked.

I'll upload the file in the comment.

Thank you very much,

Andrea