I'm studying the topic from Probabilistic Robotics by Thrun Burgard and Fox.
In the Extended Kalman Filter algorithm, we linearized the action model in the following way.
𝑔(𝑢(𝑡),𝑥(𝑡-1)) = 𝑔(𝑢(𝑡),𝜇(𝑡−1)) + 𝐺(𝑡)⋅(𝑥(𝑡−1)−𝜇(𝑡−1))
𝑔(𝑢(𝑡),𝑥(𝑡-1)) is the action model and 𝐺(𝑡) is its Jacobian matrix with respect to the state 𝑥(𝑡−1).
I don't see how this guarantees linearity because 𝑔 could be nonlinear in 𝑢(𝑡). The authors don't mention anything about why this is the case.
In other words, I imagined that the multivariate Taylor expansion for this where we get a linear function in both 𝑢(𝑡) and 𝑥(𝑡−1)