#13183: Implement index(cone) for fan morphisms
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Reporter: novoselt | Owner: mhampton
Type: enhancement | Status: new
Priority: major | Milestone: sage-5.2
Component: geometry | Keywords: toric
Work issues: | Report Upstream: N/A
Reviewers: | Authors: Andrey Novoseltsev
Merged in: | Dependencies:
Stopgaps: |
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For #12892 it would be useful to compute indices of cones as they define
the number of components of each fiber. The index is defined in
Yi Hu, Chien-Hao Liu, and Shing-Tung Yau. Toric morphisms and fibrations
of toric Calabi-Yau hypersurfaces. Adv. Theor. Math. Phys., 6(3):457-506,
2002. arXiv:math/0010082v2 [math.AG].
for the case of surjection of complete fans. The attached patch extends
the definition to any morphism:
* if the corresponded quotient of lattices is finite, return its order;
* if it has free generators, return infinity;
* if the codomain cone does not have covering domain cones at all, return
None.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13183>
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