When is the sum of closed subspaces of a Hilbert space closed?
arXiv:2012.08688
Abstract
We provide a sufficient condition for a finite number of closed subspaces of a Hilbert space to be linearly independent and their sum to be closed. Under this condition a formula for the orthogonal projection onto the sum is given. We also show that this condition is sharp (in a certain sense).
arXiv admin note: text overlap with arXiv:1606.08048