We establish lower bounds for norms and CB-norms of elementary operators on B(H ). Our main result concerns the operator T a,b x = axb + bxa and we show T a,b a b , proving a conjecture of M. Mathieu. We also establish some other results and formulae for T a,b cb and T a,b for special cases.
Norms of sampling operators
β Scribed by P. Zizler
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 264 KB
- Volume
- 277
- Category
- Article
- ISSN
- 0024-3795
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β¦ Synopsis
Let h(z) be an essentially bounded complex valued function on the unit circle Y = {z I Iz] = 1}. Consider the corresponding Laurent operator Lt, = (h= m),.meZ, where h= is the nth Fourier coefficient of h(z), h,, = fT h(z)z " dz. Let us consider an operator Sh(p,q), which we shall call a sampling operator, defined as Sh(p,q)= (hpn-qm)n,m6Z, where p, q E N = {1,2,.. ,}. These operators are obtained from Lh by "keeping" every qth column and everypth row in the bi-infinite matrix Lb. In our paper, we find an upper and lower bound for the norm of the operator Sh(p,q).
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