Kalman filter matrix G

In Estimate States of Nonlinear System with Multiple, Multirate Sensors https://www.mathworks.com/help/control/ug/multirate-nonlinear-state-estimation-in-simulink.html, x[k+1] = Ax[k]+Gw[k].

I learned Kalman filter from the book uses x=Fx+Bu and B is the control input matrix.

In matlab documentation, how do you determine G matrix? Where does Ts/2 come from??