Constrained best approximation in Hilbert space

@article{Chui1990ConstrainedBA,
  title={Constrained best approximation in Hilbert space},
  author={Charles K. Chui and Frank Deutsch and Joseph D. Ward},
  journal={Constructive Approximation},
  year={1990},
  volume={6},
  pages={35-64}
}
In this paper we study the characterization of the solution to the extremal problem inf{‖x‖x ∈C ∩M}, wherex is in a Hilbert spaceH, C is a convex cone, andM is a translate of a subspace ofH determined by interpolation conditions. We introduce a simple geometric property called the “conical hull intersection property” that provides a unifying framework for most of the basic results in the subject of optimal constrained approximation. Our approach naturally lends itself to considering the data… 
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