45 research outputs found
Truncated K-moment problems in several variables
Let be an N-dimensional real multi-sequence of
degree 2n, with associated moment matrix , and let . We prove that if
is positive semidefinite and admits a rank-preserving moment
matrix extension , then has a unique
representing measure \mu, which is r-atomic, with supp \mu\mathcal{V}(\mathcal{M}(n+1))\mathcal{M}(n+1)K_{\mathcal{Q}}\mathcal{Q}%
\equiv\{q_{i}\}_{i=1}^{m}\subseteq\mathbb{R}[t_{1},...,t_{N}]\mathcal{M}(n)\mathcal{M}(n+1)\mathcal{M}_{q_{i}}(n+[\frac{1+\deg q_{i}}{2}])(1\leq i\leq m), and \mu has precisely rank \mathcal{M}(n)-rank
\mathcal{M}_{q_{i}}(n+[\frac{1+\deg q_{i}}{2}])\mathcal{Z}(q_{i})\equiv {t\in\mathbb{R}^{N}:q_{i}(t)=0}1\leq i\leq m$.Comment: 33 pages; to appear in J. Operator Theor
Flat extensions of positive moment matrices: recursively generated relations
We develop new computational tests for existence and uniqueness of representing measures in the Truncated Complex Moment Problem: γij = Z zizj d (0 i + j 2n):(TCMP) We characterize the existence of nitely atomic representing measures in terms of positivity and extension properties of the moment matrix M(n)(γ) associated with γ γ(2n): γ00; : : : ; γ0;2n; : : : ; γ2n;0, γ00> 0 (Theorem 1.5). We study conditions for flat (i.e., rank-preserving) extensions M(n + 1) of M(n) 0; each such extension corresponds to a distinct rank M(n)-atomic representing measure, and each such measure is minimal among representing measures in terms of the cardinality of its support. For a natural class of moment matrices satisfying the tests of recursive generation, recursive consis-tency, and normal consistency, we reduce the existence problem for minimal representing measures to the solubility of small systems of multivariable alge