“…The divide and conquer technique is a popular method in distributed frameworks, where one constructs a statistic or an estimator using data in each machine, and then transmits them to the hub to get a pooled one. The divide and conquer technique has been applied successfully in many problems, including regression and classification, hypothesis testing, confidence intervals, principal eigenspaces analysis, linear discriminant analysis, and many others (Zhang et al, 2013;Hsieh et al, 2014;Zhang et al, 2015;Lin et al, 2017;SzabĂł and Van Zanten, 2019;Battey et al, 2018;Guo et al, 2019;Chen and Peng, 2018;Jordan et al, 2019;Fan et al, 2019;Tian and Gu, 2017;Li and Zhao, 2020;Dobriban and Sheng, 2021, etc. ).…”