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7 matches found
II: 11, 175-199, LNM 51 (1968)
MEYER, Paul-André
Compactifications associées à une résolvante (Potential theory)
Let $E$ be a locally compact space, $(U_p)$ be a submarkovian resolvent, with a potential kernel $U=U_0$ which maps $C_k$ (the continuous functions with compact support) into continuous bounded functions. Let $F$ be a compact space containing $E$ as a dense subset, but inducing possibly a coarser topology. It is assumed that all potentials $Uf$ with $f\in C_k$ extend to continuous functions on $F$, and that points of $F$ are separated by continuous functions on $F$ whose restriction to $E$ is supermedian. Then it is shown how to extend the resolvent to $F$ and imitate the construction of a Ray semigroup and a strong Markov process. This was an attempt to compactify the space using only supermedian functions, not $p$-supermedian for all $p>0$. An application to Markov chains is given
Comment: This method of compactification suggested by Chung's boundary theory for Markov chains (similarly Doob, Trans. Amer. Math. Soc., 149, 1970) never superseded the standard Ray-Knight approach
Keywords: Resolvents, Ray compactification, Martin boundary, Boundary theory
Nature: Original
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V: 28, 283-289, LNM 191 (1971)
WALSH, John B.
Two footnotes to a theorem of Ray (Markov processes)
Ray's theorem (Ann. of Math., 70, 1959) is the construction of a good semigroup (and process) from a Ray resolvent. The first footnote'' gives the construction of a second semigroup with nice properties from the left instead of the right side. The second footnote'' studies the filtration of a Ray process
Comment: See Meyer-Walsh, Invent. Math., 14, 1971
Keywords: Ray compactification
Nature: Original
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VI: 16, 168-172, LNM 258 (1972)
MEYER, Paul-André; WALSH, John B.
Un résultat sur les résolvantes de Ray (Markov processes)
This is a complement to the authors' paper on Ray processes in Invent. Math., 14, 1971: a lemma is proved on the existence of many martingales which are continuous whenever the process is continuous (a wrong reference for it was given in the paper). Then it is shown that the mapping $x\rightarrow P_x$ is continuous in the weak topology of measures, when the path space is given the topology of convergence in measure. Note that a correction is mentioned on the errata page of vol. VII
Comment: The idea of using the topology of convergence in measure on a path space turned out to be a fruitful idea; see Meyer and Zheng Ann. Inst. Henri Poincaré 20, 1984
Keywords: Ray compactification, Weak convergence of measures
Nature: Original
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VI: 21, 215-232, LNM 258 (1972)
WALSH, John B.
Transition functions of Markov processes (Markov processes)
Assume that a cadlag process satisfies the strong Markov property with respect to some family of kernels $P_t$ (not necessarily a semigroup). It is shown that these kernels can be modified into a true strong Markov transition function with a few additional properties. A similar problem is solved for a left continuous, moderate Markov process. The technique involves a Ray compactification which is eliminated at the end, and a useful lemma shows how to construct supermedian functions which separate points
Comment: The problem discussed here has great theoretical importance, but little practical importance except for time reversal. The construction of a nice transition function for a Markov process has been also discussed by Kuznetsov ()
Keywords: Transition functions, Strong Markov property, Moderate Markov property, Ray compactification
Nature: Original
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VII: 02, 25-32, LNM 321 (1973)
MEYER, Paul-André
Une mise au point sur les systèmes de Lévy. Remarques sur l'exposé de A. Benveniste (Markov processes)
This is an addition to the preceding paper 701, extending the theory to right processes by means of a Ray compactification
Comment: All this material has become classical. See for instance Dellacherie-Meyer, Probabilités et Potentiel, vol. D, chapter XV, 31--35
Keywords: Lévy systems, Ray compactification
Nature: Original
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VIII: 15, 289-289, LNM 381 (1974)
MEYER, Paul-André
Une note sur la compactification de Ray (Markov processes)
This short note shows that (contrary to the belief of Meyer and Walsh in a preceding paper) the state space of a Ray process is universally measurable in its Ray compactification
Comment: This is now considered a standard fact
Keywords: Ray compactification, Right processes
Nature: Original
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X: 14, 216-234, LNM 511 (1976)
WILLIAMS, David
The Q-matrix problem (Markov processes)
This paper completely solves the Q-matrix problem (find necessary and sufficient conditions for an infinite matrix $q_{ij}$ to be the pointwise derivative at $0$ of a transition matrix) in the case when all states are instantaneous. Though the statement of the problem and the two conditions given are elementary and simple, the proof uses sophisticated modern'' methods. The necessity of the conditions is proved using the Ray-Knight compactification method, the converse is a clever construction which is merely sketched
Comment: This paper crowns nearly 20 years of investigations of this problem by the English school. It contains a promise of a detailed proof which apparently was never published. See the section of Markov chains in Rogers-Williams Diffusions, Markov Processes and Martingales, vol. 1 (second edition), Wiley 1994. See also 1024
Keywords: Markov chains, Ray compactification, Local times, Excursions
Nature: Original
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