Exponential bases in L2

1971 ◽  
Vol 5 (1) ◽  
pp. 31-38 ◽  
Author(s):  
V. �. Katsnel'son
Keyword(s):  
1995 ◽  
Vol 38 (1) ◽  
pp. 171-177 ◽  
Author(s):  
Kristian Seip

It is proved that every space L2 (I1, ∪ I2), where I1 and I2 are finite intervals, has a Riesz basis of complex exponentials , {λk} a sequence of real numbers. A partial result for the corresponding problem for n≧3 finite intervals is also obtained.


2015 ◽  
pp. 509-532
Author(s):  
Fritz Gesztesy ◽  
Gilles Godefroy ◽  
Loukas Grafakos ◽  
Igor Verbitsky
Keyword(s):  

2021 ◽  
Vol 27 (5) ◽  
Author(s):  
Christina Frederick ◽  
Azita Mayeli

Author(s):  
S. A. Avdonin ◽  
S. A. Ivanov ◽  
D. L. Russell

The Fourier method in control systems reduces the study of controllability/observability to the study of related exponential families. In this paper we present examples of such systems, specifically those for which we can prove that the related exponential families form a Riesz basis in corresponding appropriately defined Sobolev spaces. This makes it possible to choose ‘natural’ pairs of spaces: the state space observability space and the control space state space, depending on whether an observation or a control problem is studied, respectively, so that the observation and control operators are isomorphisms.


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