  In this letter, we design passive beamforming in an intelligent reflecting
surface (IRS) assisted multiple-user wireless network. Two different scenarios
are considered, namely, multicasting and multi-user downlink transmission. We
optimize the passive beamforming vector of the IRS to maximize the smallest
signal-to-noise ratio of the users in both scenarios. Based on the alternating
direction method of multipliers algorithm, a low complexity method is designed
to iteratively solve the established problem. In each iteration of the proposed
method, the solution is in closed form, and thus the computation complexity is
low. Numerical results are presented to show the efficiency of the proposed
method.
