Add lbinomial function based on lbeta #99
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src/gamma.jl
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| S = float(T) | ||
| (k < 0) && return typemin(S) | ||
| if n < 0 | ||
| n = -n + k - 1 |
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Incorrect indentation here (needs one more space)
src/gamma.jl
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| (k == 0 || k == n) && return zero(S) | ||
| (k == 1) && return log(abs(n)) | ||
| if k > (n>>1) | ||
| k = n - k |
src/gamma.jl
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| end | ||
| lbinomial(n::Integer, k::Integer) = lbinomial(promote(n, k)...) | ||
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| export lbinomial |
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This should go with the other exports.
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I put it now with cosint. Not sure if this is the "normal" place or not.
test/runtests.jl
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| @@ -636,3 +636,17 @@ end | |||
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| @test beta(big(1.0),big(1.2)) ≈ beta(1.0,1.2) rtol=4*eps() | |||
| end | |||
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| @testset "lbinomial" begin | |||
| lbfixed(n) = k -> lbinomial(n, k) | |||
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Why is this necessary? You can write lbfixed(200).(0:200) below as lbinomial.(200, 0:200).
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Note that the same applies to the function defined directly below this line.
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Rebased with the corrections, dropped the lambdas in testing. |
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Thanks! |
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Is it intentional that this function is not documented? Should it be considered public API? |
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It's deprecated in favor of SpecialFunctions.jl/src/deprecated.jl Line 14 in 8136181 |
This was originally submitted to base in JuliaLang/julia#27419, but JuliaLang/julia#27473 moved
special/gamma.jlthings here, so I'm making the same PR here now. Details are copied over:This implementation of
lbinomialuses the fact thatbinomial(n,k) = 1/( (n+1) * B(n - k + 1, k + 1) ). I have added tests for some simple cases, and then also comparing for very largenwithbinomial(::BigInt, ::BigInt).The main motivation is evaluating
log(binomial(n,k))for largenwithknearn/2without approximating with Poisson:In R, this function is available as
lchoose(n, k)and is a builtin.