On scalable $K$-frames and a version of Lax-Milgram theorem

Abstract

In this paper, we first prove a theorem by a little modification on the Lax-Milgram theorem. Then, using $K$-frames, we obtain lower and upper bounds for the results obtained from this theorem. Also, we present some methods for the characterization of scalable $K$-frames. Finally, we introduce piecewise scalable $K$-frames and give necessary and sufficient conditions for a $K$-frame to be piecewise scalable.