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Reconfigurable intelligent surface (RIS) becomes an increasingly important technology in sixth-generation (6G). The key aspect of RIS is smartly configuring the wireless propagation environment and providing supplementary links to enhance the signal transmission between the BS and the UE. In recent years, there has been a surge of interest in RISs in joint active and passive beamforming design to improve the system performance of RIS-assisted systems with the assumption of uncorrelated environments. To date, far too little attention has been paid to the situations that consider the correlations among the antennas and RIS reflecting elements. In this article, we focus on an RIS-assisted multiple-input multiple-output (MIMO) system under spatial fading correlations, with the statistical channel state information (CSI) known at the transmitter and the RIS. We aim to maximize the ergodic spectral efficiency (SE) of …