#13700: fix non-crystallographic "example" of Dynkin diagram
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Reporter: hthomas | Owner: sage-combinat
Type: defect | Status: new
Priority: minor | Milestone: sage-5.5
Component: combinatorics | Keywords: root system, Dynkin diagram
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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!DynkinDiagram().an_instance() returns something that isn't a Dynkin
diagram, in the sense that it is non-crystallographic, i.e., its Cartan
matrix is not symmetrizable.
{{{
sage: X=DynkinDiagram().an_instance()
sage: X.cartan_matrix()
[ 2 -1 -1]
[-2 2 -1]
[-1 -1 2]
sage: X.cartan_matrix().is_symmetrizable()
False
}}}
It will be trivial to fix this.
I wonder if the "add_edge()" method should be changed -- as it stands, it
is easy for the user to create instances of !DynkinDiagram() which will
not in fact be Dynkin diagrams, as this example shows.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13700>
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