#17157: Cleanup formula for Bell numbers
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Reporter: jdemeyer | Owner:
Type: enhancement | Status: new
Priority: minor | Milestone: sage-6.4
Component: combinatorics | Keywords:
Merged in: | Authors: Jeroen Demeyer
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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In the function `bell_number`, we have the line
{{{
return ZZ(ceil(N((b - n) / n2 * exp2(Integer(-1)) - 1 / 4, log(b, 2) +
3)))
}}}
This can be improved by
1. Removing the `1 / 4` which is actually `0` in Python 2.
2. Not using global functions like `ceil()` and `exp()`.
3. Using a `RealField` instead of the `N()` function.
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Ticket URL: <http://trac.sagemath.org/ticket/17157>
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