#9972: Add fan morphisms
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Reporter: novoselt | Owner: mhampton
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-4.6
Component: geometry | Keywords:
Author: Andrey Novoseltsev | Upstream: N/A
Reviewer: Volker Braun | Merged:
Work_issues: implement preimage_cones |
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Changes (by novoselt):
* work_issues: switch to FanMorphism => implement preimage_cones
Old description:
> This patch adds classes for toric lattices homspaces and homomorphisms
> and allows checking fan compatibility and automatic subdivision to
> achieve this compatibility.
>
> See #9604 for prerequisites.
New description:
This patch adds a module for fan morphisms - morphisms between lattices
with specified fans in the domain and codomain, which are compatible with
this morphism. Compatibility check and automatic construction of the
codomain fan or refinement of the domain fan are implemented.
See #9604 for prerequisites.
--
Comment:
I am attaching a patch that does not compute `preimage_cones` yet, but the
rest is claimed to be ready for review/comments. I have removed classes
for lattice morphisms themselves since they were not adding anything
anymore. All of the old functionality is moved to `FanMorphism`
constructor as you have suggested above. Codomain fan can now be omitted
and will be computed, if possible.
This feature has exposed a problem I mentioned (I think) when we were
adding warnings to the `Fan` constructor. The image fan is generated by
images of cones of the original fan and these images may coincide or
become non-maximal. As a result, one of the doctests fails due to the
warning that some cones were discarded and users may see such a message as
well, which will be quite confusing, I think. What should we do? Add a
parameter to `Fan(..., warn=True)` and set it to `False` explicitly in the
internal code?
Current queue:
* trac_9972_add_cone_embedding.patch
* trac_9972_improve_element_constructors.patch
* trac_9972_remove_enhanced_cones_and_fans.patch
* trac_9972_add_fan_morphisms.patch
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9972#comment:44>
Sage <http://www.sagemath.org>
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