#14972: charpoly name clashes with matrix content
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Reporter: gagern | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-5.12
Component: linear algebra | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Dependencies:
Stopgaps: |
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Comment (by nbruin):
I think always requiring a variable name (or a polynomial ring or
something similar) is the "right" thing to do: in sage, there is no such
thing as "the" polynomial ring over a given ring, so there is no way to
choose a canonical default. Variable names are an essential ingredient for
a polynomial ring and since a characteristic polynomial has to live in
one, this name has to be specified somehow.
It might be that the "right" thing is considered too pedantic for general
use, though (certainly now that people have gotten used to not having to
specify a variable).
Trying to come up with a non-clashing name would be a kludge and makes me
think of one of the rules of the Zen of Python: "in the face of ambiguity,
refuse the temptation to guess", which tends to be a pretty good guideline
for interface design.
One would hope that the polynomial ring in which the charpol is returned
would be at least a function of the parent of the matrix, but as we see,
that is already not possible for SR.
If it is deemed a default choice for varname is necessary to keep the sage
interface bearable then I would be in favour of making a very cheap
choice: just "x" or "t" or some other reasonable looking name ("lambda" is
painful because it's a keyword in python).
--
Ticket URL: <http://trac.sagemath.org/ticket/14972#comment:2>
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