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The truncated complex K-moment problem
Journal article   Open access   Peer reviewed

The truncated complex K-moment problem

Raúl Curto and Lawrence A. Fialkow
Transactions of the American Mathematical Society, Vol.352(6), pp.2825-2855
01/01/2000
DOI: 10.1090/s0002-9947-00-02472-7
url
https://doi.org/10.1090/s0002-9947-00-02472-7View
Published (Version of record) Open Access

Abstract

Let γ ≡ γ(2n) denote a sequence of complex numbers γ00 , γ01 , γ10, . . . , γ0,2n , . . . , γ2n,0 (γ00 > 0, γij = ¯γji), and let K denote a closed subset of the complex plane C. The Truncated Complex K-Moment Problem for γ entails determining whether there exists a positive Borel mea- sure μ on C such that γij = ∫ ¯zizj dμ (0 ≤ i + j ≤ 2n) and supp μ ⊆ K. For K ≡ KP a semi-algebraic set determined by a collection of complex poly- nomials P = {pi (z, ¯z)}m i=1, we characterize the existence of a finitely atomic representing measure with the fewest possible atoms in terms of positivity and extension properties of the moment matrix M (n) (γ) and the localizing matri- ces Mpi . We prove that there exists a rank M (n)-atomic representing measure for γ(2n) supported in KP if and only if M (n) ≥ 0 and there is some rank- preserving extension M (n + 1) for which Mpi (n + ki) ≥ 0, where deg pi = 2ki or 2ki − 1 (1 ≤ i ≤ m).
Flat extensions of positive matrices Localizing matrix Moment matrix extension Semi-algebraic sets Truncated complex moment problem

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