Motivated by the well-known Papoulis-Gerchberg algorithm, an iterative thresholding algorithm for recovery of sparse signals from few observations is proposed. The sequence of iterates turns out to be similar to that of the thresholded Landweber iterations, although not the same. The performance of the proposed algorithm is experimentally evaluated and compared to other state-of-the-art methods.

We explore the C2-equivariant spectra Tmf1(3) and TMF1(3). In particular, we compute their C2-equivariant Picard groups and the C2-equivariant Anderson dual of Tmf1(3). This implies corresponding results for the fixed point spectra TMF0(3) and Tmf0(3). Furthermore, we prove a Real Landweber exact functor theorem.

1. Cohomology theories: definition, examples including ordinary cohomology, K-theory and cobordism. 2. Products and operations: motivation, definitions and examples (especially K-theory). 3. New theories from old: splittings, Bousfield localization, formal group laws and the Landweber exact functor theorem. 4. Relationships between theories: some natural transformations, the chromatic viewpoint...

We construct the algebraic stack of formal groups and use it to provide a new perspective onto a recent result of M. Hovey and N. Strickland on comodule categories for Landweber exact algebras. This leads to a geometric understanding of their results as well as to a generalisation.