Math problem

[hjwdzh]

I have a math problem with the equation at the last line of page 8 in the paper .

Atv = -At(A H.inv At).inv A H.inv Jt f

Typically, when I approximate H with diag(H), this will happen

Atv = -At(A Hinv At)inv A H.inv Jt f = -At (At.inv H A.inv) A H.inv Jt f = -Jt f

Put it into eq 9 and I will get delta X = 0, which apparently is incorrect.

Would you let me know what is wrong with my mathematics?