5 citations · 8 across the 12 of their papers we have counts for
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When is the sum of closed subspaces of a Hilbert space closed?
Ivan Feshchenko
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 f…
On the inverse best approximation property of systems of subspaces of a Hilbert space
Ivan Feshchenko
Let be a Hilbert space and be closed subspaces of . Denote by the orthogonal projection onto , . Following Patrick L. Combettes and Nol…
On the optimal error bound for the first step in the method of cyclic alternating projections
Ivan Feshchenko
Let be a Hilbert space and be closed subspaces of . Set and let be the orthogonal projection onto , .…
When is the sum of complemented subspaces complemented?
Ivan Feshchenko
We provide a sufficient condition for the sum of a finite number of complemented subspaces of a Banach space to be complemented. Under this condition a formula for a projection ont…
On the closedness of the sum of ranges of operators with almost compact products
Ivan S. Feshchenko
Let be complex Hilbert spaces and be a bounded linear operator with the closed range ,…
On the essential spectrum of the sum of self-adjoint operators and the closedness of the sum of operator ranges
Ivan S. Feshchenko
We get a criterion for 0 to be in the essential spectrum of a sum of self-adjoint operators whose pairwise products are compact. Using this result, we obtain necessary and sufficie…