66 research outputs found
The Powerdomain of Indexed Valuations
This paper is about combining nondeterminism and probabilities. We study this phenomenon from a domain theoretic point of view. In domain theory, nondeterminism is modeled using the notion of powerdomain, while probability is modeled using the powerdomain of valuations. Those two functors do not combine well, as they are. We define the notion of powerdomain of indexed valuations, which can be combined nicely with the usual nondeterministic powerdomain. We show an equational characterization of our construction. Finally we discuss the computational meaning of indexed valuations, and we show how they can be used, by giving a denotational semantics of a simple imperative language
A localic theory of lower and upper integrals
An account of lower and upper integration is given. It is constructive in the sense of geometric logic. If the integrand takes its values in the non-negative lower reals, then its lower integral with respect to a valuation is a lower real. If the integrand takes its values in the non-negative upper reals,then its upper integral with respect to a covaluation and with domain of
integration bounded by a compact subspace is an upper real. Spaces of valuations and of covaluations are defined.
Riemann and Choquet integrals can be calculated in terms of these lower and upper integrals
Integrals and Valuations
We construct a homeomorphism between the compact regular locale of integrals
on a Riesz space and the locale of (valuations) on its spectrum. In fact, we
construct two geometric theories and show that they are biinterpretable. The
constructions are elementary and tightly connected to the Riesz space
structure.Comment: Submitted for publication 15/05/0
Semantic Domains for Combining Probability and Non-Determinism
AbstractWe present domain-theoretic models that support both probabilistic and nondeterministic choice. In [A. McIver and C. Morgan. Partial correctness for probablistic demonic programs. Theoretical Computer Science, 266:513–541, 2001], Morgan and McIver developed an ad hoc semantics for a simple imperative language with both probabilistic and nondeterministic choice operators over a discrete state space, using domain-theoretic tools. We present a model also using domain theory in the sense of D.S. Scott (see e.g. [G. Gierz, K. H. Hofmann, K. Keimel, J. D. Lawson, M. W. Mislove, and D. S. Scott. Continuous Lattices and Domains, volume 93 of Encyclopedia of Mathematics and its Applications. Cambridge University Press, Cambridge, 2003]), but built over quite general continuous domains instead of discrete state spaces.Our construction combines the well-known domains modelling nondeterminism – the lower, upper and convex powerdomains, with the probabilistic powerdomain of Jones and Plotkin [C. Jones and G. Plotkin. A probabilistic powerdomain of evaluations. In Proceedings of the Fourth Annual Symposium on Logic in Computer Science, pages 186–195. IEEE Computer Society Press, 1989] modelling probabilistic choice. The results are variants of the upper, lower and convex powerdomains over the probabilistic powerdomain (see Chapter 4). In order to prove the desired universal equational properties of these combined powerdomains, we develop sandwich and separation theorems of Hahn-Banach type for Scott-continuous linear, sub- and superlinear functionals on continuous directed complete partially ordered cones, endowed with their Scott topologies, in analogy to the corresponding theorems for topological vector spaces in functional analysis (see Chapter 3). In the end, we show that our semantic domains work well for the language used by Morgan and McIver
Stochastic order on metric spaces and the ordered Kantorovich monad
In earlier work, we had introduced the Kantorovich probability monad on
complete metric spaces, extending a construction due to van Breugel. Here we
extend the Kantorovich monad further to a certain class of ordered metric
spaces, by endowing the spaces of probability measures with the usual
stochastic order. It can be considered a metric analogue of the probabilistic
powerdomain.
The spaces we consider, which we call L-ordered, are spaces where the order
satisfies a mild compatibility condition with the metric itself, rather than
merely with the underlying topology. As we show, this is related to the theory
of Lawvere metric spaces, in which the partial order structure is induced by
the zero distances.
We show that the algebras of the ordered Kantorovich monad are the closed
convex subsets of Banach spaces equipped with a closed positive cone, with
algebra morphisms given by the short and monotone affine maps. Considering the
category of L-ordered metric spaces as a locally posetal 2-category, the lax
and oplax algebra morphisms are exactly the concave and convex short maps,
respectively.
In the unordered case, we had identified the Wasserstein space as the colimit
of the spaces of empirical distributions of finite sequences. We prove that
this extends to the ordered setting as well by showing that the stochastic
order arises by completing the order between the finite sequences, generalizing
a recent result of Lawson. The proof holds on any metric space equipped with a
closed partial order.Comment: 49 pages. Removed incorrect statement (Theorem 6.1.10 of previous
version
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