109 research outputs found
Cardinal interpolation and spline fucntions V. The B-splines for cardinal Hermite interpolation
AbstractIn the third paper of this series on cardinal spline interpolation [4] Lipow and Schoenberg study the problem of Hermite interpolation S(v) = Yv, SâČ(v) = YvâČ,âŠ,S(râ1)(v) = Yv(râ1) for allv. The B-splines are there conspicuous by their absence, although they were found very useful for the case Îł = 1 of ordinary (or Lagrange) interpolation (see [5â10]). The purpose of the present paper is to investigate the B-splines for the case of Hermite interpolation (Îł > 1). In this sense the present paper is a supplement to [4] and is based on its results. This is done in Part I. Part II is devoted to the special case when we want to solve the problem S(v) = Yv, SâČ(v) = YvâČ for all v by quintic spline functions of the class CâŽ(â â, â). This is the simplest nontrivial example for the general theory. In Part II we derive an explicit solution for the problem (1), where v = 0, 1,âŠ, n
A topological interpretation of the walk distances
The walk distances in graphs have no direct interpretation in terms of walk
weights, since they are introduced via the \emph{logarithms} of walk weights.
Only in the limiting cases where the logarithms vanish such representations
follow straightforwardly. The interpretation proposed in this paper rests on
the identity \ln\det B=\tr\ln B applied to the cofactors of the matrix
where is the weighted adjacency matrix of a weighted multigraph and
is a sufficiently small positive parameter. In addition, this
interpretation is based on the power series expansion of the logarithm of a
matrix. Kasteleyn (1967) was probably the first to apply the foregoing approach
to expanding the determinant of . We show that using a certain linear
transformation the same approach can be extended to the cofactors of
which provides a topological interpretation of the walk distances.Comment: 13 pages, 1 figure. Version #
Euclidean Distances, soft and spectral Clustering on Weighted Graphs
We define a class of Euclidean distances on weighted graphs, enabling to
perform thermodynamic soft graph clustering. The class can be constructed form
the "raw coordinates" encountered in spectral clustering, and can be extended
by means of higher-dimensional embeddings (Schoenberg transformations).
Geographical flow data, properly conditioned, illustrate the procedure as well
as visualization aspects.Comment: accepted for presentation (and further publication) at the ECML PKDD
2010 conferenc
Möbius characterization of hemispheres
In this paper we generalize the Möbius characterization of metric spheres as obtained in Foertsch and Schroeder [4] to a corresponding Möbius characterization of metric hemispheres
On spherical averages of radial basis functions
A radial basis function (RBF) has the general form
where the coefficients a 1,âŠ,a n are real numbers, the points, or centres, b 1,âŠ,b n lie in â d , and Ï:â d ââ is a radially symmetric function. Such approximants are highly useful and enjoy rich theoretical properties; see, for instance (Buhmann, Radial Basis Functions: Theory and Implementations, [2003]; Fasshauer, Meshfree Approximation Methods with Matlab, [2007]; Light and Cheney, A Course in Approximation Theory, [2000]; or Wendland, Scattered Data Approximation, [2004]). The important special case of polyharmonic splines results when Ï is the fundamental solution of the iterated Laplacian operator, and this class includes the Euclidean norm Ï(x)=âxâ when d is an odd positive integer, the thin plate spline Ï(x)=âxâ2log ââxâ when d is an even positive integer, and univariate splines. Now B-splines generate a compactly supported basis for univariate spline spaces, but an analyticity argument implies that a nontrivial polyharmonic spline generated by (1.1) cannot be compactly supported when d>1. However, a pioneering paper of Jackson (Constr. Approx. 4:243â264, [1988]) established that the spherical average of a radial basis function generated by the Euclidean norm can be compactly supported when the centres and coefficients satisfy certain moment conditions; Jackson then used this compactly supported spherical average to construct approximate identities, with which he was then able to derive some of the earliest uniform convergence results for a class of radial basis functions. Our work extends this earlier analysis, but our technique is entirely novel, and applies to all polyharmonic splines. Furthermore, we observe that the technique provides yet another way to generate compactly supported, radially symmetric, positive definite functions. Specifically, we find that the spherical averaging operator commutes with the Fourier transform operator, and we are then able to identify Fourier transforms of compactly supported functions using the PaleyâWiener theorem. Furthermore, the use of Haar measure on compact Lie groups would not have occurred without frequent exposure to Iserlesâs study of geometric integration
Metric trees of generalized roundness one
Every finite metric tree has generalized roundness strictly greater than one.
On the other hand, some countable metric trees have generalized roundness
precisely one. The purpose of this paper is to identify some large classes of
countable metric trees that have generalized roundness precisely one.
At the outset we consider spherically symmetric trees endowed with the usual
combinatorial metric (SSTs). Using a simple geometric argument we show how to
determine decent upper bounds on the generalized roundness of finite SSTs that
depend only on the downward degree sequence of the tree in question. By
considering limits it follows that if the downward degree sequence of a SST satisfies , then has generalized roundness one. Included among the
trees that satisfy this condition are all complete -ary trees of depth
(), all -regular trees () and inductive limits
of Cantor trees.
The remainder of the paper deals with two classes of countable metric trees
of generalized roundness one whose members are not, in general, spherically
symmetric. The first such class of trees are merely required to spread out at a
sufficient rate (with a restriction on the number of leaves) and the second
such class of trees resemble infinite combs.Comment: 14 pages, 2 figures, 2 table
Metric Möbius geometry and a characterization of spheres
We obtain a Möbius characterization of the n-dimensional spheres Sn endowed with the chordal metric d0. We show that every compact extended Ptolemy metric space with the property that every three points are contained in a circle is Möbius equivalent to (Sn, d0) for some n ℠1
- âŠ