Changes between Version 2 and Version 3 of Ticket #26966, comment 28


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Timestamp:
01/10/19 00:20:26 (6 months ago)
Author:
jhpalmieri
Comment:

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  • Ticket #26966, comment 28

    v2 v3  
    33sage: K = SimplicialComplex([[1.0 + 2^-52, 1.0]])
    44sage: L = K.product(K)
    5 sage: K.set_immutable()
    6 sage: L.set_immutable()
    75sage: d = Hom(K,L).diagonal_morphism()
    8 sage: d.induced_homology_morphism()
     6sage: d.associated_chain_complex_morphism()
    97---------------------------------------------------------------------------
    108ValueError                                Traceback (most recent call last)
     
    1311}}}
    1412
    15 Edit: this case is actually worse because in the product `L`, the vertices are named using string representations, so there is only one vertex, not four, as there should be. (Each vertex is named `'L1.00000000000000R1.00000000000000'`, and since they all have the same name, they are viewed as the same vertex.) You can avoid this by using `L = K.product(K, rename_vertices=False)`, but then the diagonal map is not defined: it relies on the vertex names coming from `rename_vertices=True`.
     13Edit: this case is actually worse because in the product `L`, the vertices are named using string representations, so there is only one vertex, not four, as there should be. (Each vertex is named `'L1.00000000000000R1.00000000000000'`, and since they all have the same name, they are viewed as the same vertex.) You can avoid this as follows:
     14{{{
     15sage: K = SimplicialComplex([[1.0 + 2^-52, 1.0]])
     16sage: L = K.product(K, rename_vertices=False)
     17sage: d = Hom(K,L).diagonal_morphism(rename_vertices=False)
     18sage: d.associated_chain_complex_morphism()
     19---------------------------------------------------------------------------
     20ValueError                                Traceback (most recent call last)
     21...
     22ValueError: matrices must define a chain complex morphism
     23}}}
     24Now the names of the vertices cause bad sorting, and so the purported map `d` does not induce a chain map as it should. This is the same problem that arises with other complexes if we don't sort at all.