Wednesday, 05 May 2021, 14:00 at Online (Join Zoom Meeting https://us02web.zoom.us/j/81608191565?pwd=RDR2Uk1pU1Y3bHdZV3Q0SFlWdVYzdz09) – The set of matrices of a certain size and rank is a smooth manifold. Unfortunately, it is not closed: this is uncomfortable for optimization. The closure of that manifold, namely, the set of matrices with bounded rank, is an algebraic variety but it is not smooth. That also is uncomfortable …