#17123: Extending binomial(n,k) to negative integers n, k.
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Reporter: pluschny | Owner:
Type: enhancement | Status: new
Priority: minor | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: binomial | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
Volker, it actually seems to me that the change is not totally straight
forward.
There is the `_eval_` method, and the `_evalf_` method. Probably both need
to be changed.
And there is the `_binomial_sym` method. Will this need a change as well?
It currently returns zero if the second argument is negative:
{{{
sage: binomial._binomial_sym(x,-5)
0
}}}
Should the return value be a different symbolic expression? After all, the
value (according to the formula in the ticket description) is not zero if
x evaluates to a negative number that is greater or equal to `-5`.
So, here I don't know a good answer.
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Ticket URL: <http://trac.sagemath.org/ticket/17123#comment:7>
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