DSelect-k: Differentiable Selection in the Mixture of Experts with Applications to Multi-Task Learning - Hazimeh, Hussein; Zhao, Zhe; Chowdhery, Aakanksha; Sathiamoorthy, Maheswaran; Chen, Yihua; Mazumder, Rahul; Hong, Lichan; Chi, Ed (Advances in Neural Information Processing Systems, 2021)