University of Ulm,
Faculty of Computer Science,
Dept. PM,
up: People
Publications
- W. Gehring, P. Salamon, R.E.Whitney, P. Sibani
Correlation structure of landscapes of NP-complete optimization
problems at finite temperature
We analyze the autocorrelation function of a time series of energy values sampled in
the energy landscapes of four different combinatorial optimization problems by a
Metropolis random walk. The temperature of the walk and the size of the investigated
problems are systematically varied. We find that, in a suitably defined high
temperature region the autocorrelation decays in an exponential fashion. We extract
the temperature and system size dependence of the corresponding correlation time,
which turns out to be of the Arrhenius form. Energetic and entropic contributions to
the correlation time (barriers) are identified and shown to be asymptotically
independent of system size.
Open Systems & Information Dynamics. Volume 11, Issue 2, June 2004,
Pages 177-184, ISSN 1230-1612.
- Wolfgang Gehring
A Mapping of XML Schema Types To C#
This paper proposes a mapping from XML Schema Definition
Language (XSD) to C#. XSDs are the type system of XML. In XSD,
many more types can be defined than in C# or a comparable
programming language. C#'s class library provides many classes
for creation and manipulation of XML objects; however, C# does
not support the XSD type system (like native C# types). We thus
propose a mapping which maps XSDs to C#. The mapping is injective
such that all semantically meaningful information in the schema is
maintained. C# properties are used to ensure restrictions on
types that have no native counterpart in C#.
- Wolfgang Gehring
On why C#'s type system needs an extension
Class libraries of
object-oriented programming languages like C# provide many
classes for creation and manipulation of XML objects; however,
they do not support the XSD type system like native types. In XSD,
many more types can be defined than in today's object-oriented
programming languages. In this paper, we look at a few examples of
why and where there are mismatches between the two worlds of XML
and OO in order to motivate why the type system of C# and related
OO-languages needs to be extended.
- Wolfgang Gehring
A framework for the introduction of credit point systems (in German)
As a reaction to the increasing competition in higher education the
German conference of university presidents (Hochschulrektorenkonferenz)
and the conference of the ministers of education (Kultusministerkonferenz)
recommend the introduction of credit point systems at German universities.
This is also explicitly included in the new University Law of the state of
Baden-Württemberg.
Since credit point systems are a fairly new idea to German universities,
however, it is to a large degree unclear what
measures have to be taken to introduce such credit point systems.
This framework wants to help to remedy this situation. It is a
guideline for the introduction of credit point systems; it offers
support and can also serve as a reference book. We aim for a
credit accumulation and transfer system which is to a degree modeled
after ECTS (the European Credit Transfer System). Overall, credit
point systems are expected to make a significant contribution to
quality assurance in both learning and teaching at institutions of
higher education.
2. revised and extended edition, April 2002
ISBN 3-89559-078-9
- P. Salamon, P. Sibani, W. Gehring, R.E.Whitney, R. Frost
Toward a taxonomy of NP-hard combinatorial optimization problems
It is argued that a taxonomy of hard combinatorial problems is needed to
better understand the performance of heuristic search algorithms based
on physical or biological analogies. We describe several methods of
gathering useful information for identifying classification schemes.
Statistical methods based on Monte Carlo sampling can yield the
thermodynamic portrait of the problem as well as the temperature
dependent autocorrelation function of the time series of energies.
Exhaustive enumeration methods based on exploring the neighborhood
of local minima can give the local density of states. Both the
autocorrelation function and the local density of states show
simple exponential behaviour for a large class of problems.
Bulletin of the American Physical Society, Volume 43, No.1, March 1998
See also
here.
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