Results 81 to 90 of about 21,084 (200)

A Conforming Least Squares Approach for the Numerical Approximation of Parabolic Equations

Proceedings in Applied Mathematics and Mechanics, Volume 25, Issue 4, December 2025.
ABSTRACT We propose a least squares formulation for the numerical approximation of parabolic partial differential equations, which minimizes the residual of the equation using the natural L2(0,T;H−1(Ω))$L^2(0,T;H^{-1}(\Omega))$ norm. In particular, we avoid making regularity assumptions on the problem's data.
Michael Hinze, Christian Kahle, Michael Stahl   +2 more
wiley   +1 more source

On Almost Orthogonal Frames

International Journal of Mathematics and Mathematical Sciences, 2012
Almost orthogonal frames have been introduced and studied. It has been proved that a bounded almost orthogonal frame satisfies Feichtinger conjecture. Also, we prove that a bounded almost orthogonal frame contains a Riesz basis.
Virender, A. Zothansanga, S. K. Kaushik
doaj   +1 more source

Fractional Q$Q$‐curvature on the sphere and optimal partitions

Journal of the London Mathematical Society, Volume 112, Issue 6, December 2025.
Abstract We study an optimal partition problem on the sphere, where the cost functional is associated with the fractional Q$Q$‐curvature in terms of the conformal fractional Laplacian on the sphere. By leveraging symmetries, we prove the existence of a symmetric minimal partition through a variational approach. A key ingredient in our analysis is a new
Héctor A. Chang‐Lara, Juan Carlos Fernández, Alberto Saldaña   +2 more
wiley   +1 more source

Characterizing the R-duality of g-frames

Journal of Inequalities and Applications, 2019
In this paper, we define the g-Riesz-dual of a given special operator-valued sequence with respect to g-orthonormal bases for a separable Hilbert space.
Liang Li, Pengtong Li
doaj   +1 more source

The domination theorem for operator classes generated by Orlicz spaces

Mathematische Nachrichten, Volume 298, Issue 11, Page 3576-3598, November 2025.
Abstract We study lattice summing operators between Banach spaces focusing on two classes, ℓφ$\ell _\varphi$‐summing and strongly φ$\varphi$‐summing operators, which are generated by Orlicz sequence lattices ℓφ$\ell _\varphi$. For the class of strongly φ$\varphi$‐summing operators, we prove the domination theorem, which complements Pietsch's ...
D. L. Fernandez, M. Mastyło, J. Santos, E. B. Silva   +3 more
wiley   +1 more source

Sufficient conditions for functions to form Riesz bases in L_2 and applications to nonlinear boundary-value problems

Electronic Journal of Differential Equations, 2001
We find sufficient conditions for systems of functions to be Riesz bases in $L_2(0,1)$. Then we improve a theorem presented in [13] by showing that a ``standard'' system of solutions of a nonlinear boundary-value problem, normalized to 1, is a Riesz ...
Peter E. Zhidkov
doaj  

The nonlocal boundary value problem with perturbations of mixed boundary conditions for an elliptic equation with constant coefficients. I

Karpatsʹkì Matematičnì Publìkacìï, 2019
In this article we investigate a problem with nonlocal boundary conditions which are multipoint perturbations of mixed boundary conditions in the unit square $G$ using the Fourier method. The properties of a generalized transformation operator $R: L_2(G)
Ya.O. Baranetskij, P.I. Kalenyuk, M.I. Kopach, A.V. Solomko   +3 more
doaj   +1 more source

Global and microlocal aspects of Dirac operators: Propagators and Hadamard states

Mathematische Nachrichten, Volume 298, Issue 9, Page 2942-2974, September 2025.
Abstract We propose a geometric approach to construct the Cauchy evolution operator for the Lorentzian Dirac operator on Cauchy‐compact globally hyperbolic 4‐manifolds. We realize the Cauchy evolution operator as the sum of two invariantly defined oscillatory integrals—the positive and negative Dirac propagators—global in space and in time, with ...
Matteo Capoferri, Simone Murro
wiley   +1 more source

The nonlocal problem for the $2n$ differential equations with unbounded operator coefficients and the involution

Karpatsʹkì Matematičnì Publìkacìï, 2018
We study a problem with periodic boundary conditions for a $2n$-order differential equation whose coefficients are non-self-adjoint operators. It is established that the operator of the problem has two invariant subspaces generated by the involution ...
Ya.O. Baranetskij, I.I. Demkiv, I.Ya. Ivasiuk, M.I. Kopach   +3 more
doaj   +1 more source