This article aims to give an intuitive introduction to operator semi-groups and their generators from a probabilistic perspective. By ‘intuitive’ it is meant that the article relies mainly on heuristics and analogies to make its points. For example the definition of the generator is motivated from an analogy to the Cauchy functional equation g(t + s) = g(t)g(s) for real-valued functions. No pro...

Semi-invertible multiplicative ergodic theorems establish the existence of an Oseledets splitting for cocycles of non-invertible linear operators (such as transfer operators) over an invertible base. Using a constructive approach, we establish a semi-invertible multiplicative ergodic theorem that for the first time can be applied to the study of transfer operators associated to the composition ...

The charge-current density and two-photon operators consistent with a single-particle semi-relativistic Hamiltonian are derived within a suitable functional derivative formalism which preserves gauge invariance. An application to electron scattering is presented and results are compared with a fully relativistic case and the non-relativistic cases corrected through fourth order in M−1.

Let A be a bounded operator on a separable, infinite dimensional Hilbert space H. Moreover, assume that A is not in the set C + K(H) of operators expressible as a sum of a scalar multiple of identity and a compact operator. What is the smallest similarity invariant semigroup containing operator A? Equivalently, which operators can be expressed as products of operators, similar to A? A partial a...

This paper presents an abstract analysis of bounded variation (BY) methods for illposed apentor equations Au = L. Let where the penalty, or 'regularization'. parameter (I > 0 and the functional J ( u ) is the BY norm or semi-norm of U , also known 3s the total variation of U. Under mild restrictions on the operator A and the functional J ( u ) , it is shown that the functional T ( u ) has a uni...

In this paper, we study the semi-discrete Galerkin finite element method for parabolic equations with Lipschitz continuous coefficients. We prove the maximumnorm stability of the semigroup generated by the corresponding elliptic finite element operator, and prove the space-time stability of the parabolic projection onto the finite element space in L∞(QT ) and L p((0, T ); Lq ( )), 1 < p, q < ∞....