Geometric multiscale decompositions of dynamic low-rank matrices

The present paper is concerned with the study of manifold-valued multiscale transforms with a focus on the Stiefel manifold. For this specific geometry we derive several formulas and algorithms for the computation of geometric means which will later enable us to construct multiscale transforms of wavelet type. As an application we study compression of piecewise smooth families of low-rank matrices both for synthetic data and also real-world data arising in hyperspectral imaging. As a main theoretical contribution we show that the manifold-valued wavelet transforms can achieve an optimal N -term approximation rate for piecewise smooth functions with possible discontinuities. This latter result is valid for arbitrary manifolds. AMS Subject Classification: primary 42C40, 65N12 secondary 65N15, 65N30, 42C99