Quadratically hyponormal weighted shifts with two equal weights
The planar set \({\mathcal R}\) of all pairs \((x,y)\) with the property that the weighted shift \(W_{1,(1,\sqrt x,\sqrt y)^{\wedge}}\) is positively quadratically hyponormal is shown to be closed convex with nonempty interior. The boundary of \({\mathcal R}\) is also described in terms of these data.
scientific article; zbMATH DE number 1507907
scientific article