A Note on Parallel Preconditioning for the All-at-Once Solution of Riesz Fractional Diffusion Equations - Xian-Ming Gu, Xian-Ming Gu; Bruno Carpentieri, Bruno Carpentieri; Yong-Liang Zhao, Yong-Liang Zhao; Yu-Yun Huang, Yu-Yun Huang; Xi-Le Zhao, Xi-Le Zhao (Numerical Mathematics: Theory, Methods and Applications, 2021)