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arXiv 1001.3679math.FAmath.RA
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截断迹矩问题

The truncated tracial moment problem

Sabine Burgdorf, Igor Klep

摘要:

我们提出的tracial类似的经典结果Curto和Fialkow矩矩阵。一个由非交换变量中的字索引的实数序列,其值在索引的轮换下不变,称为迹序列。我们证明了这样一个序列可以用矩阵的迹矩表示,如果它对应的矩矩阵是半正定的,且是有限秩的。截断迹序列允许这样的表示,当且仅当它的一个扩展允许平坦扩展。最后,我们应用对偶理论研究了非对易变量的迹正多项式。

英文摘要:

We present tracial analogs of the classical results of Curto and Fialkow on moment matrices. A sequence of real numbers indexed by words in non-commuting variables with values invariant under cyclic permutations of the indexes, is called a tracial sequence. We prove that such a sequence can be represented with tracial moments of matrices if its corresponding moment matrix is positive semidefinite and of finite rank. A truncated tracial sequence allows for such a representation if and only if one of its extensions admits a flat extension. Finally, we apply the theory via duality to investigate trace-positive polynomials in non-commuting variables.

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