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A tutorial on EMPA: A theory of concurrent processes with nondeterminism, priorities, probabilities and time
 Theoretical Computer Science
, 1998
"... In this tutorial we give an overview of the process algebra EMPA, a calculus devised in order to model and analyze features of realworld concurrent systems such as nondeterminism, priorities, probabilities and time, with a particular emphasis on performance evaluation. The purpose of this tutorial ..."
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Cited by 103 (9 self)
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In this tutorial we give an overview of the process algebra EMPA, a calculus devised in order to model and analyze features of realworld concurrent systems such as nondeterminism, priorities, probabilities and time, with a particular emphasis on performance evaluation. The purpose of this tutorial is to explain the design choices behind the development of EMPA and how the four features above interact, and to show that a reasonable trade off between the expressive power of the calculus and the complexity of its underlying theory has been achieved.
An Efficient Approach to Removing Geometric Degeneracies (Extended Abstract)
, 1992
"... Our aim is to perturb the input so that an algorithm designed under the hypothesis of input nondegeneracy can execute on arbitrary instances. The deterministic scheme of [EmCa] was the first efficient method and was applied to two important predicates. Here it is extended in a consistent manner to ..."
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Cited by 36 (4 self)
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Our aim is to perturb the input so that an algorithm designed under the hypothesis of input nondegeneracy can execute on arbitrary instances. The deterministic scheme of [EmCa] was the first efficient method and was applied to two important predicates. Here it is extended in a consistent manner to another two common predicates, thus making it valid for most algorithms in computational geometry. It is shown that this scheme incurs no extra algebraic complexity over the original algorithm while it increases the bit complexity by a factor roughly proportional to the dimension of the geometric space. The second contribution of this paper is a variant scheme for a restricted class of algorithms that is asymptotically optimal with respect to the algebraic as well as the bit complexity. Both methods are simple to implement and require no symbolic computation. They also conform to certain criteria ensuring that the solution to the original input can be restored from the output on the perturbed input. This is immediate when the input to solution mapping obeys a continuity property and requires some casespecific work otherwise. Finally we discuss extensions and limitations to our approach.
DBranes on CalabiYau Manifolds and Superpotentials
, 2002
"... We show how to compute terms in an expansion of the worldvolume superpotential for fairly general Dbranes on the quintic CalabiYau using linear sigma model techniques, and show in examples that this superpotential captures the geometry and obstruction theory of bundles and sheaves on this Calabi ..."
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Cited by 19 (3 self)
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We show how to compute terms in an expansion of the worldvolume superpotential for fairly general Dbranes on the quintic CalabiYau using linear sigma model techniques, and show in examples that this superpotential captures the geometry and obstruction theory of bundles and sheaves on this CalabiYau.
Neighborly cubical polytopes
 Discrete & Computational Geometry
, 2000
"... Neighborly cubical polytopes exist: for any n ≥ d ≥ 2r + 2, there is a cubical whose rskeleton is combinatorially equivalent to that of the convex dpolytope Cn d ndimensional cube. This solves a problem of Babson, Billera & Chan. Kalai conjectured that the boundary ∂Cn d of a neighborly cubic ..."
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Cited by 11 (1 self)
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Neighborly cubical polytopes exist: for any n ≥ d ≥ 2r + 2, there is a cubical whose rskeleton is combinatorially equivalent to that of the convex dpolytope Cn d ndimensional cube. This solves a problem of Babson, Billera & Chan. Kalai conjectured that the boundary ∂Cn d of a neighborly cubical polytope Cn d maximizes the fvector among all cubical (d − 1)spheres with 2n vertices. While we show that this is true for polytopal spheres if n ≤ d+1, we also give a counterexample for d = 4 and n = 6. Further, the existence of neighborly cubical polytopes shows that the graph of the ndimensional cube, where n ≥ 5, is “dimensionally ambiguous ” in the sense of Grünbaum. We also show that the graph of the 5cube is “strongly 4ambiguous”. In the special case d = 4, neighborly cubical polytopes have f3 = f0 4 log2 f0 4 vertices, so the facetvertex ratio f3/f0 is not bounded; this solves a problem of Kalai, Perles and Stanley studied by Jockusch.
Affine tangles and irreducible exotic sheaves
, 802
"... Abstract. We construct a weak representation of the category of framed affine tangles on a disjoint union of triangulated categories D2n. The categories we use are that of coherent sheaves on Springer fibers over a nilpotent element of sl2n with two equal Jordan blocks. This representation allows us ..."
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Cited by 1 (0 self)
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Abstract. We construct a weak representation of the category of framed affine tangles on a disjoint union of triangulated categories D2n. The categories we use are that of coherent sheaves on Springer fibers over a nilpotent element of sl2n with two equal Jordan blocks. This representation allows us to enumerate the irreducible objects in the heart of the exotic tstructure on D2n by crossingless matchings of 2n points on a circle. We also describe the algebra of endomorphisms of the direct sum of the irreducible objects. 1.
Leftleaning RedBlack Trees
"... The redblack tree model for implementing balanced search trees, introduced by Guibas and Sedgewick thirty years ago, is now found throughout our computational infrastructure. Redblack trees are described in standard textbooks and are the underlying data structure for symboltable implementations w ..."
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The redblack tree model for implementing balanced search trees, introduced by Guibas and Sedgewick thirty years ago, is now found throughout our computational infrastructure. Redblack trees are described in standard textbooks and are the underlying data structure for symboltable implementations within C++, Java, Python, BSD Unix, and many other modern systems. However, many of these implementations have sacrificed some of the original design goals (primarily in order to develop an effective implementation of the delete operation, which was incompletely specified in the original paper), so a new look is worthwhile. In this paper, we describe a new variant of redblack trees that meets many of the original design goals and leads to substantially simpler code for insert/delete, less than onefourth as much code as in implementations in common use. All redblack trees are based on implementing 23 or 234 trees within a binary tree, using red links to bind together internal nodes into 3nodes or 4nodes. The new code is based on combining three ideas: • Use a recursive implementation. • Require that all 3nodes lean left.
unknown title
, 2003
"... A new general purpose event horizon finder for 3D numerical spacetimes ..."
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Collective Coordinates For Ion Dynamics
, 1994
"... Utilising a link between microfield smoothness and ion dynamics, a method for calculating the autocorrelation function of spectral line shapes in a plasma, including ion dynamics, is presented. The method is based on a time \Gamma independent simulation, in that the dynamics are handled semianalyt ..."
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Utilising a link between microfield smoothness and ion dynamics, a method for calculating the autocorrelation function of spectral line shapes in a plasma, including ion dynamics, is presented. The method is based on a time \Gamma independent simulation, in that the dynamics are handled semianalytically via a separable kernel approximation in Dyson's equation. For each perturber configuration this reduces to the solution of a linear algebraic system. In addition this method naturally leads to a set of (approximate) relevant collective coordinates. It is shown that the microfield must be smooth and this implies the existence of new collective coordinates, namely the microfield values at a few time points. Nonsmooth components are separated out and treated analytically by the ion impact theory. This approach is valid for all parameter ranges and may be utilized either as an alternative to solving the Schrodinger equation in a simulationlike manner, or by using the collective coordinat...