10,951 research outputs found
Finding problems in knowledge bases using modal logics
In this paper I propose that it is suitable to consider some statements that an expert makes during knowledge elicitation as being statements in a modal logic. This approach gives us several advantages in finding inconsistencies between a knowledge base and an expert's intuition in her field. I illustrate this approach by using the modal logic VC, a logic of counterfactual conditionals. In an appendix, I give brief details of theorem proving in VC
No evidence for an early seventeenth-century Indian sighting of Keplers supernova (SN1604)
In a recent paper Sule et al. (Astronomical Notes, vol. 332 (2011), 655)
argued that an early 17th-century Indian mural of the constellation Sagittarius
with a dragon-headed tail indicated that the bright supernova of 1604 was also
sighted by Indian astronomers. In this paper it will be shown that this
identification is based on a misunderstanding of traditional Islamic
astrological iconography and that the claim that the mural represents an early
17th-century Indian sighting of the supernova of 1604 has to be rejected.Comment: 7 pages, 6 figures. To appear in Astronomical Notes, vol. 334, issue
5 (2013), DOI number 1172
An Empirical Analysis of Search in GSAT
We describe an extensive study of search in GSAT, an approximation procedure
for propositional satisfiability. GSAT performs greedy hill-climbing on the
number of satisfied clauses in a truth assignment. Our experiments provide a
more complete picture of GSAT's search than previous accounts. We describe in
detail the two phases of search: rapid hill-climbing followed by a long plateau
search. We demonstrate that when applied to randomly generated 3SAT problems,
there is a very simple scaling with problem size for both the mean number of
satisfied clauses and the mean branching rate. Our results allow us to make
detailed numerical conjectures about the length of the hill-climbing phase, the
average gradient of this phase, and to conjecture that both the average score
and average branching rate decay exponentially during plateau search. We end by
showing how these results can be used to direct future theoretical analysis.
This work provides a case study of how computer experiments can be used to
improve understanding of the theoretical properties of algorithms.Comment: See http://www.jair.org/ for any accompanying file
Three editions of the Star Catalogue of Tycho Brahe
Tycho Brahe completed his catalogue with the positions and magnitudes of 1004
fixed stars in 1598. This catalogue circulated in manuscript form. Brahe edited
a shorter version with 777 stars, printed in 1602, and Kepler edited the full
catalogue of 1004 stars, printed in 1627. We provide machine-readable versions
of the three versions of the catalogue, describe the differences between them
and briefly discuss their accuracy on the basis of comparison with modern data
from the Hipparcos Catalogue. We also compare our results with earlier analyses
by Dreyer (1916) and Rawlins (1993), finding good overall agreement. The
magnitudes given by Brahe correlate well with modern values, his longitudes and
latitudes have error distributions with widths of about 2 arcmin, with excess
numbers of stars with larger errors (as compared to Gaussian distributions), in
particular for the faintest stars. Errors in positions larger than 10 arcmin,
which comprise about 15 per cent of the entries, are likely due to computing or
copying errors.Comment: Accepted by Astronomy and Astrophysics; 24 pages; 63 figures; 3
machine readable tables made available at CD
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