目的研究Hilbert空间H上的Hilbert基、Bessel基、Riesz基三者间的关系,及其与Bessel列、小波Riesz基的关系。方法算子论方法。结果证明了对于Hilbert空间H的任一Schuder基{xn},序列{xn+xn^*}是H的一个Besselian基且{xn+xn^*}≥{xn},{xn+xn^*}≥{xn^*}。结论对于H的任一Schuder基{xn},定义U(xn+xn^*)=xn^*,则{xn}是H的一个Besselian基当且仅当‖U‖〈1,而且给出了Riesz基的5个等价刻画。
Aim To discuss some relationships between several bases for a Hilbert space H,including Hilbertian bases,Besselian bases and Riesz bases,Bessel sequences and wavelet Riesz bases in wavelet analysis.Methods Using some methods of operator theory.Results Let {xn} be a Schuder basis for a Hilbert space H,it is proved that the sequence {xn+xn^*} is always a Bseeslian basis for H with the properties {xn+xn^*}≥{xn} and {xn+xn^*}≥{xn^*},where {xn^*} is the coeffient functions of {xn}.Conclusion {xn} is a Besselian basis for H if and only if ‖U‖〈1,where U is the operator defined by U(xn+xn^*)=xn^*,and it is got that five conditions are equivalent for Riesz basis.