bpo-35431: Implemented math.comb by FR4NKESTI3N · Pull Request #11414 · python/cpython (original) (raw)
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Implemented the function math.comb to calculate binomial coefficient. Simple O(k) algorithm is used for now. ValueError if condition 0 <= k <= n is not satisfied and TypeError if non-integer arguments passed to function.
https://bugs.python.org/issue35431
bpo-35434: Implemented math.comb bpo-35431: Implemented math.comb
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You can use Jebelean’s exact division algorithm to speed up the division as if you factor out the coefficients as the product of(n-k+1)* PROD(i,2,k,(n-k+i)/i), i will always divide the already calculated product.
KellerFuchs added a commit to KellerFuchs/cpython that referenced this pull request
@FR4NKESTI3N Thanks a lot for starting on this. I merged our PRs in #11018, as the testsuite I had started there was more complete (and used as the basis for discussing the desired behaviour, in the bugs.python.org issue).
PS: I added you as a collaborator on my repository, so if you accept the invite you can push directly to that PR's branch.
A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.
Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.
I have made the requested changes; please review again
@rhettinger I have used long_long instead of long in the boilerplate.
Using object allowed evaluation of expressions like comb(10**400, 200) and overflow was caused if min(k, n-k) was larger than LLONG_MAX. I feel using object conversion gave the function more flexibility.
Thanks for making the requested changes!
@rhettinger: please review the changes made to this pull request.
KellerFuchs added a commit to KellerFuchs/cpython that referenced this pull request
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- Use
PyNumber_Index()for converting arguments to Python integers. Seegcd()for example. - Do not convert
nto C long long.comb(2**1000, 5)should work. - Do not use
PyNumber_Long().
It is convenient to implement perm(n, k) first. comb(n, k) can be easily implemented as perm(n, k) // factorial(k) (or perm(n, n-k) // factorial(n-k) if k > n-k).
@serhiy-storchaka So boilerplate should be changed back to have n and k as objects right?
@KellerFuchs I will be busy for 2 weeks, can you get in on this.
DinoV pushed a commit to DinoV/cpython that referenced this pull request
