Smoothness analysis of subdivision algorithms
In computer graphics, subdivision algorithms are common tools for smoothing down irregularly shaped meshes. Of special... more
In computer graphics, subdivision algorithms are common tools for smoothing down irregularly shaped meshes. Of special interest, due to their simple formulations, are algorithms that generalize B-spline subdivision. Their conceptual simplicity is in stark contrast to the complexity of analysing their results. A complete formal examination of smoothness properties for subdivision schemes was only recently performed by Jörg Peters and Ulrich Reif.
This thesis presents a precise and detailed introduction to the analysis of subdivision algorithms. For this purpose, first of all, the necessary background in B-spline theory is established. Building on this, two of the most common subdivision algorithms, the Doo-Sabin and the Catmull-Clark scheme, are motivated. Their treatment is followed by an in-depth description of methods for analysing smoothness properties of subdivision schemes, as developed by Peters and Reif. Afterwards, these methods are applied to the two aforementioned algorithms, thereby establishing smoothness for both algorithms in their original form. Last, in order to demonstrate the effects of choosing unsuitable weights, a number of degenerate weights, which produce irregular shapes in almost all cases, are derived for both schemes—these have hitherto not been published.
Fatgraph Algorithms and the Homology of the Kontsevich Complex
Pre-print available on arXiv: http://arxiv.org/abs/1202.1820
Fatgraphs are multigraphs enriched with a cyclic order of the edgesvincident to a vertex. This paper presents... more
Fatgraphs are multigraphs enriched with a cyclic order of the edgesvincident to a vertex. This paper presents algorithms to:
(1) generate the set of fatgraphs, given the genus and the number of boundary cycles;
(2) compute automorphisms of any given fatgraph;
(3) compute the homology of the fatgraph complex.
The algorithms are suitable for effective computer implementation.
In particular, this allows us to compute the rational homology of
the moduli space of Riemann surfaces with marked points. We thus compute the Betti numbers of $M_{g,n}$ with $(2g + n) \leq 6$.
Geometries of the imaginary - Developing of architectural design from M.C. Escher’s and Buckminter Fuller’s formal research,
co-authored with Giovanni Ferrero, Celestina Cotti, Cecilia Tedeschi, published in Nexusjournal, 11/2, Birkauser, 2009
The long search of M.C. Escher in order to decode the geometric meant of the space among mathematical truth,... more
The long search of M.C. Escher in order to decode the geometric meant of the space among mathematical truth, perception and representation, developes itself through some compenetrating topics:
- geometric structure of the landscape, as continuity between morphology and architecture;
- metamorphosis between shapes, ideas or living species in the evolutionary chain;
- rappresentazione of the temporal dimension, also in the ambiguity of the point of view.
The common denominator of this search is the intention to give a shape to the concept of “infinite” that lies toghether unit and variety: the rappresentazione becomes cosmogonia, like a secular image of the creation.
If the sensory knowledge caught up through the perception is illusory, the explanation of the geometric structure of the space through rigorous logic of the mathematical rationality is real and concrete.
The image of the infinite takes shape in the drake biting its tail, in the Moebius’ strips, in the spirals or in the compositions of circles and the squares according to Coxeter’s surface. These forms, sophisticated in their mathematician reference are tied to iniziatory symbols, and ancestral designs.
But the Escher’s graphical inventions are reflected from the work of a contemporary American inventor, who was extremely pragmatic and visionary at the same time. Buckminster Fuller, half architect and half engineer, went on studing spatial simmetries of the platonic solids, in order to resolve the problems of the construction and applies space geometries to the planning of light, industrialized and transportable structures.
To the time of the Cold War its geodetic domes become the symbol of the technology of the West, but his imagination was not pleased of the architectonic construction and he extends this model to the rappresentazione of the land surface, with the licence of one innovative cartographic projection, specifically thought for the air navigation on orthodromic routes.
Fuller’s buildings give concretness to architectural concerns of Escher’s mathematical representations, who trought his graphic constructions based on hiperbolic geometry, opens new ways related to non linear transformations in groups theories. This work means investigate how architectural design may develope new geometries.
References
M.C. Escher, His life and complete graphic work, Abrasale Press, New York, 1982.
Michael J. Gorman, Buckminster Fuller Architettura in movimento, Skira, Ginevra-Milano, 2005
Frucht, R., Graphs of degree three with a given abstract group, Canadian J. Math. 1, pgg. 365-378 (1949)
Klein, F. Vergleichende Betrachtung ueber neue geometriche Forschungen, Program, Erlangen, 1872
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Topological rewriting and the geometrization of programming.
Jean-Louis Giavitto and Antoine Spicher. Topological rewriting and the geometrization of programming. Physica D, 237:1302–1314, 2008.
Spatial computing is an emerging field that recognizes the importance of explicitly handling spatial relationships at... more Spatial computing is an emerging field that recognizes the importance of explicitly handling spatial relationships at three levels: computer architectures, programming languages and applications. In this context, we present MGS, an experimental programming language where data structures are fields on abstract spaces. In MGS, fields are transformed using rules. We show that this approach is able to unify, at least for programming purposes, several computational models like Lindenmayer systems and cellular automata. The MGS notions of topological collection and transformation are formalized using concepts developed in algebraic topology. We propose to use transformations in order to implement a discrete version of some differential operators. These transformations satisfy a Stokes-like theorem. This result constitutes a geometric view of programming where data are handled like fields in physics. The relevance of this approach for the design of autonomic software systems is discussed in the conclusion
Topological rewriting and the geometrization of programming.
Jean-Louis Giavitto and Antoine Spicher. Topological rewriting and the geometrization of programming. Physica D, 237:1302–1314, 2008.
Spatial computing is an emerging field that recognizes the importance of explicitly handling spatial relationships at... more Spatial computing is an emerging field that recognizes the importance of explicitly handling spatial relationships at three levels: computer architectures, programming languages and applications. In this context, we present MGS, an experimental programming language where data structures are fields on abstract spaces. In MGS, fields are transformed using rules. We show that this approach is able to unify, at least for programming purposes, several computational models like Lindenmayer systems and cellular automata. The MGS notions of topological collection and transformation are formalized using concepts developed in algebraic topology. We propose to use transformations in order to implement a discrete version of some differential operators. These transformations satisfy a Stokes-like theorem. This result constitutes a geometric view of programming where data are handled like fields in physics. The relevance of this approach for the design of autonomic software systems is discussed in the conclusion
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