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 |
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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: |

### Description

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) 0 sage: qa.q_binomial(2,3) 1/(q^2 + q + 1) sage: binomial(2,3) 0

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.

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