{"title":"紧凑算子的纳亚克定理","authors":"B V Rajarama Bhat, Neeru Bala","doi":"arxiv-2408.16994","DOIUrl":null,"url":null,"abstract":"Let $A$ be an $m\\times m$ complex matrix and let $\\lambda _1, \\lambda _2,\n\\ldots , \\lambda _m$ be the eigenvalues of $A$ arranged such that $|\\lambda\n_1|\\geq |\\lambda _2|\\geq \\cdots \\geq |\\lambda _m|$ and for $n\\geq 1,$ let\n$s^{(n)}_1\\geq s^{(n)}_2\\geq \\cdots \\geq s^{(n)}_m$ be the singular values of\n$A^n$. Then a famous theorem of Yamamoto (1967) states that $$\\lim _{n\\to\n\\infty}(s^{(n)}_j )^{\\frac{1}{n}}= |\\lambda _j|, ~~\\forall \\,1\\leq j\\leq m.$$\nRecently S. Nayak strengthened this result very significantly by showing that\nthe sequence of matrices $|A^n|^{\\frac{1}{n}}$ itself converges to a positive\nmatrix $B$ whose eigenvalues are $|\\lambda _1|,|\\lambda _2|,$ $\\ldots ,\n|\\lambda _m|.$ Here this theorem has been extended to arbitrary compact\noperators on infinite dimensional complex separable Hilbert spaces. The proof\nmakes use of Nayak's theorem, Stone-Weirstrass theorem, Borel-Caratheodory\ntheorem and some technical results of Anselone and Palmer on collectively\ncompact operators. Simple examples show that the result does not hold for\ngeneral bounded operators.","PeriodicalId":501036,"journal":{"name":"arXiv - MATH - Functional Analysis","volume":"14 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Nayak's theorem for compact operators\",\"authors\":\"B V Rajarama Bhat, Neeru Bala\",\"doi\":\"arxiv-2408.16994\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Let $A$ be an $m\\\\times m$ complex matrix and let $\\\\lambda _1, \\\\lambda _2,\\n\\\\ldots , \\\\lambda _m$ be the eigenvalues of $A$ arranged such that $|\\\\lambda\\n_1|\\\\geq |\\\\lambda _2|\\\\geq \\\\cdots \\\\geq |\\\\lambda _m|$ and for $n\\\\geq 1,$ let\\n$s^{(n)}_1\\\\geq s^{(n)}_2\\\\geq \\\\cdots \\\\geq s^{(n)}_m$ be the singular values of\\n$A^n$. Then a famous theorem of Yamamoto (1967) states that $$\\\\lim _{n\\\\to\\n\\\\infty}(s^{(n)}_j )^{\\\\frac{1}{n}}= |\\\\lambda _j|, ~~\\\\forall \\\\,1\\\\leq j\\\\leq m.$$\\nRecently S. Nayak strengthened this result very significantly by showing that\\nthe sequence of matrices $|A^n|^{\\\\frac{1}{n}}$ itself converges to a positive\\nmatrix $B$ whose eigenvalues are $|\\\\lambda _1|,|\\\\lambda _2|,$ $\\\\ldots ,\\n|\\\\lambda _m|.$ Here this theorem has been extended to arbitrary compact\\noperators on infinite dimensional complex separable Hilbert spaces. The proof\\nmakes use of Nayak's theorem, Stone-Weirstrass theorem, Borel-Caratheodory\\ntheorem and some technical results of Anselone and Palmer on collectively\\ncompact operators. Simple examples show that the result does not hold for\\ngeneral bounded operators.\",\"PeriodicalId\":501036,\"journal\":{\"name\":\"arXiv - MATH - Functional Analysis\",\"volume\":\"14 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-08-30\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"arXiv - MATH - Functional Analysis\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/arxiv-2408.16994\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - MATH - Functional Analysis","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2408.16994","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Let $A$ be an $m\times m$ complex matrix and let $\lambda _1, \lambda _2,
\ldots , \lambda _m$ be the eigenvalues of $A$ arranged such that $|\lambda
_1|\geq |\lambda _2|\geq \cdots \geq |\lambda _m|$ and for $n\geq 1,$ let
$s^{(n)}_1\geq s^{(n)}_2\geq \cdots \geq s^{(n)}_m$ be the singular values of
$A^n$. Then a famous theorem of Yamamoto (1967) states that $$\lim _{n\to
\infty}(s^{(n)}_j )^{\frac{1}{n}}= |\lambda _j|, ~~\forall \,1\leq j\leq m.$$
Recently S. Nayak strengthened this result very significantly by showing that
the sequence of matrices $|A^n|^{\frac{1}{n}}$ itself converges to a positive
matrix $B$ whose eigenvalues are $|\lambda _1|,|\lambda _2|,$ $\ldots ,
|\lambda _m|.$ Here this theorem has been extended to arbitrary compact
operators on infinite dimensional complex separable Hilbert spaces. The proof
makes use of Nayak's theorem, Stone-Weirstrass theorem, Borel-Caratheodory
theorem and some technical results of Anselone and Palmer on collectively
compact operators. Simple examples show that the result does not hold for
general bounded operators.