where B = A−1 − 3
2EV −1EH. Obviously the Lyapunov
function (23) converges if B is positive definite. It can be
verified that (22) is a sufficient condition for positive definite
B. Hence Theorem 1 is proved.
Remark 2: For the general case with MUI, (16) involves
updating extra dual variables associated with (19). Let {βl, l =
1, ...,L} be the stepsizes in updating these dual variables.
It can be proved similarly that the condition in Theorem 1
becomes