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arxiv: 1303.4972 · v1 · pith:ROUHL3BWnew · submitted 2013-03-20 · 🧮 math.FA

On left democracy function

classification 🧮 math.FA
keywords basisgreedyleftcitedemocracyfunctionlambdanon-doubling
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We continue the study undertaken in \cite{GHN} of left democracy function $h_l(N)=\inf_{#\Lambda=N}\left\|\sum_{n\in \Lambda_N} x_n\right\| $ of an unconditional basis in a Banach space $X$. We provide an example of a basis with $h_l$ non-doubling. Then we show that for bases with non-doubling $h_l$ the greedy projection is not optimal. Together with results from \cite{GHN} and improved by C. Cabrelli, G. Garrig\'os, E. Hernandez and U. Molter we get that the basis is greedy if and only if the greedy projection is optimal.

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