Abspoel, M.A.
(2009)
Computing homology of subcomplexes of the 3torus.
Bachelor's Thesis, Mathematics.
Abstract
Suppose one has a collection of large geometric objects and one wishes to differentiate between them. When taking measurements on an object, one can probably only get a finite approximation of the object. It is not always possible to fully reconstruct what the original object looked like from this approximation. However, we can compute certain characteristics of the object.
This thesis deals with computing some of these characteristics, called homology groups. The approximations we use are simplicial complexes. We use a fast incremental algorithm by Delfinado and Edelsbrunner for computing simplicial homology over Z2 for subcomplexes of the 3sphere. These complexes include simplicial approximations of objects realized in ordinary 3dimensional space. The algorithm outputs the Betti numbers of a complex. These numbers are the ranks of the homology groups, and they uniquely identify the homology group.
Many approximating data sets, however, are periodic. We therefore adapt the algorithm to work with subcomplexes of the 3torus. To use the algorithm, we need to expand subcomplexes of the 3torus to complete triangulations of the 3torus. A method is developed to accomplish this.
The adapted algorithm is shown to be approximately correct: the true first and second Betti numbers can be at most three higher than the computed ones. For large simplicial complexes this incremental algorithm might be more practical than the already available slower methods which provide a more accurate output.
Item Type: 
Thesis
(Bachelor's Thesis)

Supervisor: 
Supervisor name  Supervisor E mail 

Vegter, G.  UNSPECIFIED 

Degree programme: 
Mathematics 
Thesis type: 
Bachelor's Thesis 
Language: 
English 
Date Deposited: 
15 Feb 2018 07:28 
Last Modified: 
17 Apr 2019 12:35 
URI: 
http://fse.studenttheses.ub.rug.nl/id/eprint/8584 
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