科研之友
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摘要
Let mu be a finite positive measure on the real line. For a > 0, denote by epsilon(a) the family of exponential functions epsilon(a) - {epsilon(ist) vertical bar s is an element of[0, a]}. The exponential type of mu is the infimum of all numbers a such that the finite linear combinations of the exponentials from epsilon(a) are dense in L-2 (mu). If the set of such a is empty, the exponential type of mu is defined as infinity. The well-known type problem asks to find the exponential type of mu in terms of mu. In this note we present a solution to the type problem and discuss its relations with known results.
- 出版日期2013-11
