Opened 9 years ago

Last modified 9 years ago

#11411 closed defect

some q binomial coefficients should be zero — at Initial Version

Reported by: chapoton Owned by: sage-combinat
Priority: minor Milestone: sage-4.7.2
Component: combinatorics Keywords:
Cc: chapoton, sage-combinat Merged in:
Authors: Reviewers:
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:


I have found the following behaviour:

sage: import sage.combinat.q_analogues as qa
sage: qa.q_binomial(2,-1)
1/(q^2 + q + 1)
sage: binomial(2,-1)
sage: qa.q_binomial(2,3)
1/(q^2 + q + 1)
sage: binomial(2,3)

I think these q-binomials should rather be zero. The q-binomial is based on the q-factorial, where one finds the following behaviour

sage: [qa.q_factorial(-i) for i in range(6)]
[1, 1, 1, 1, 1, 1]

This seems to be rather wrong, as the factorial itself is infinite for negative integers.

Change History (1)

Changed 9 years ago by chapoton

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