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Wold-type extension for N-tuples of commuting contractions

100%

Kosiek M., Octavio A.

Studia Mathematica

1999

tom 137

nr 1

81-91

Let (T_1,…,T_N) be an N-tuple of commuting contractions on a separable, complex, infinite-dimensional Hilbert space ℋ. We obtain the existence of a commuting N-tuple (V_1,…,V_N) of contractions on a superspace K of ℋ such that each $V_j$ extends $T_j$, j=1,…,N, and the N-tuple (V_1,…,V_N) has a decomposition similar to the Wold-von Neumann decomposition for coisometries (although the $V_j$ need not be coisometries). As an application, we obtain a new proof of a result of Słociński (see [9])

Another formulation of the Wick’s theorem. Farewell, pairing?

100%

Beloussov I. V.

Special Matrices

2015

tom 3

nr 1

The algebraic formulation of Wick’s theorem that allows one to present the vacuum or thermal averages of the chronological product of an arbitrary number of field operators as a determinant (permanent) of the matrix is proposed. Each element of the matrix is the average of the chronological product of only two operators. This formulation is extremely convenient for practical calculations in quantum field theory, statistical physics, and quantum chemistry by the standard packages of the well known computer algebra systems.

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On the Existence of Common Fixed Points for Semigroups of Nonlinear Mappings in Modular Function Spaces

63%

Kozlowski W. M.

Commentationes Mathematicae

2011

tom 51

nr 1

Let $C$ be a $\rho$-bounded, $\rho$-closed, convex subset of a modular function space $L_\rho$. We investigate the existence of common fixed points for semigroups of nonlinear mappings $T_t\colon C\to C$, i.e. a family such that $T_0(x) = x$, $T_{s+t} = T_s (T_t (x))$, where each $T_t$ is either $\rho$-contraction or $\rho$-nonexpansive. We also briefly discuss existence of such semigroups and touch upon applications to differential equations.

Ograniczanie wyników

1 Commentationes Mathematicae

1 Special Matrices

1 Studia Mathematica

1 Beloussov I. V.

1 Kosiek M.

1 Kozlowski W. M.

1 Octavio A.

1 2015

1 2011

1 1999

Wyniki wyszukiwania

Wold-type extension for N-tuples of commuting contractions

Another formulation of the Wick’s theorem. Farewell, pairing?

On the Existence of Common Fixed Points for Semigroups of Nonlinear Mappings in Modular Function Spaces