Un algorithme pour calculer l’invariant de Walker. (An algorithm for the computation of Walker’s invariant). (French) Zbl 0718.57007

K. Walker [Bull. Am. Math. Soc., New Ser. 22, 261-267 (1990; Zbl 0699.57008)] has extended A. Casson’s \({\mathbb{Z}}\)-valued invariant, defined for oriented integral homology 3-spheres, to a \({\mathbb{Q}}\)-valued invariant \(\lambda\) (M) defined for an arbitrary oriented rational homology 3- sphere (RHS) M. An important part of his theory is his surgery formula which, for RHS’s M and N such that N is obtained from M by a Dehn surgery along a knot in M, expresses \(\lambda\) (N)-\(\lambda\) (M) in terms of the surgery data. In the present paper the author develops a programmable algorithm for calculating \(\lambda\) (M) for an RHS M which is given in terms of a surgery diagram, i.e. a link diagram D with a rational ‘weight’ assigned to each of its components such that the Dehn surgery on \(S^ 3\) along D using the ‘weights’ as surgery coefficients (or ‘framing numbers’) produces M. She first shows how to replace D by another surgery diagram, \(D'\), for M and how to order the components of \(D'\) so that if one does the Dehn surgeries along the components of \(D'\) (in the chosen order) one at a time, all intermediate manifolds are RHS’s. Then she describes how one can calculate the surgery data (which appear in Walker’s surgery formula) of all these one-component surgeries in terms of \(D'\) and its ‘weights’.


57N10 Topology of general \(3\)-manifolds (MSC2010)
57N12 Topology of the Euclidean \(3\)-space and the \(3\)-sphere (MSC2010)
57R65 Surgery and handlebodies


Zbl 0699.57008
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