A counter-example to a conjecture of Friedland |
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Authors: | Takashi Yoshino |
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Affiliation: | 1. Department of Mathematics, College of General Education, T?hoku University, Kawauchi, Aoba-ku, 980, Sendai, Japan
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Abstract: | In 1982, S. Friedland proved that a bounded linear operator A on a Hilbert space is normal if and only if (αI + A + A*)2 ≧ AA* − A*A ≧ −(αI + A + A*)2 for all real α. And he conjectured the inequality (αI + A + A*)2 ≧ AA* − A*A for all real α will imply that A*A − AA* ≧ 0, i.e., A is hyponormal. But his conjecture is incorrect. In this note I’ll give a counter-example for his conjecture. |
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