“…Initially explored in the setting of subspace packing problems [30,5,16], the application of Stiefel and Grassmann manifolds has become widespread in computer vision and pattern recognition. Examples include: video processing arXiv:2006.14086v1 [cs.CV] 24 Jun 2020 A PREPRINT -JUNE 26, 2020 [12], classification, [11,4,33,34], action recognition [2], expression analysis [31,32,17], domain adaptation [15,28], regression [29,13], pattern recognition [18], and computation of subspace means [3,22]. More recently, Grassmannians have also been explored in the deep neural network literature [14].…”