کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4599735 1631151 2014 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
On the Gau–Wu number for some classes of matrices
موضوعات مرتبط
مهندسی و علوم پایه ریاضیات اعداد جبر و تئوری
پیش نمایش صفحه اول مقاله
On the Gau–Wu number for some classes of matrices
چکیده انگلیسی

For a given n×nn×n matrix A  , let k(A)k(A) stand for the maximal number of orthonormal vectors xjxj such that the scalar products 〈Axj,xj〉〈Axj,xj〉 lie on the boundary of the numerical range W(A)W(A). This number was recently introduced by Gau and Wu and we therefore call it the Gau–Wu number of the matrix A  . We compute k(A)k(A) for two classes of n×nn×n matrices A  . A simple and explicit expression for k(A)k(A) for tridiagonal Toeplitz matrices A   is derived. Furthermore, we prove that k(A)=2k(A)=2 for every pure almost normal matrix A. Note that for every matrix A   we have k(A)⩾2k(A)⩾2, and for normal matrices A   we have k(A)=nk(A)=n, so our results show that pure almost normal matrices are in fact as far from normal as possible with respect to the Gau–Wu number. Finally, matrices with maximal Gau–Wu number (k(A)=nk(A)=n) are considered.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Linear Algebra and its Applications - Volume 444, 1 March 2014, Pages 254–262
نویسندگان
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