I have a question about the Newton optimization with Tikhonov regularization used in your paper

[HMCCMH]

First, thanks for your excellent job!
Could you tell me how to infer the formula (21) in the paper of RBGT. I remember that g equals (J(x)^T)*f(x). However, the g^T in the formula (24) equals J(x). (J(x) is the jacobian matrix) The value of f(x) seems to be not multiplied into the formula. I know that f(x) is the probabilistic function, which is shown in the formula (16).
Or f(θ) equals 1 when θ=0？