| Revista Colombiana de Matemáticas |
|
Volumen 28
[2]
(1994)Páginas 83-91 |
Abstract. Necessary and sufficient conditions are given for the numerical range of a bounded space operator to have an empty interior. A sufficient condition for this set to be open is also established.
Palabras claves. Hilbert and pre-Hilbert spaces; bounded, self-adjoint and normal operators; interior of a set; numerical range and spectrum of an operator; functions of class C^1