We prove that a strong geometrical condition (the unit ball is the balanced convex hull of a uniformly strongly exposed set), introduced by J. Lindenstrauss to deal with norm-attaining operators, is ...

The Rocky Mountain Journal of Mathematics, Vol. 41, No. 3 (2011), pp. 813-832 (20 pages) The classical numerical range of a quadratic operator is an elliptical disk. This result is extended to ...