TANDEM: Bi-Level Data Mixture Optimization with Twin Networks - Wang, Jiaxing; Xiang, Deping; Xu, Jin; Yi, Mingyang; Gong, Guoqiang; Zhang, Zicheng; Li, Haoran; Liu, Pengzhang; Chen, Zhen; Zhang, Ke; Fan, Ju; Jiang, Qixia (Advances in Neural Information Processing Systems, 2025)