id: 06003184 dt: j an: 06003184 au: Hadani, Ronny; Singer, Amit ti: Representation theoretic patterns in three-dimensional cryo-electron microscopy. II: The class averaging problem. so: Found. Comput. Math. 11, No. 5, 589-616 (2011). py: 2011 pu: Springer-Verlag, New York, NY la: EN cc: ut: differential geometry; spectral theory; optimization theory; mathematical biology; 3D cryo-electron microscopy ci: Zbl 1216.92046; Zbl 1227.92036 li: doi:10.1007/s10208-011-9095-3 ab: Summary: We study the formal algebraic structure underlying the intrinsic classification algorithm, recently introduced by {\it A. Singer} et al. [SIAM J. Imaging Sci. 4, No. 2, 723‒759 (2011; Zbl 1216.92046)], for classifying noisy projection images of similar viewing directions in three-dimensional cryo-electron microscopy (cryo-EM). This preliminary classification is of fundamental importance in determining the three-dimensional structure of macromolecules from cryo-EM images. Inspecting this algebraic structure we obtain a conceptual explanation for the admissibility (correctness) of the algorithm and a proof of its numerical stability. The proof relies on studying the spectral properties of an integral operator of geometric origin on the two-dimensional sphere, called the localized parallel transport operator. Along that way, we continue to develop the representation theoretic set-up for three-dimensional cryo-EM that was initiated by the authors in part I of this paper [Ann. Math. (2) 174, No. 2, 1219‒1241 (2011; Zbl 1227.92036)]. rv: