2 D ec 1 99 5 APPROXIMATION BY ANALYTIC MATRIX FUNCTIONS . THE FOUR BLOCK PROBLEM VLADIMIR
نویسنده
چکیده
The problem of approximating a given scalar function φ on the unit circle T uniformly by functions analytic in the unit disk D has been attracting analysts for a long time (see [Kha], [RSh], [Ne], [AAK1-2], [CJ], [PKh]). It was shown in [Kha] that for a continuous function φ such a best approximation is unique while it is not unique in the general case. Later it turned out that this problem is closely related with Hankel operators. Namely, it was proved by Nehari [Ne] that
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