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[math] improve Binomial function #18509

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Merged
guitargeek merged 5 commits into from
Apr 28, 2025
Merged

[math] improve Binomial function #18509

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8390afa
[nfc] improve binomial docu
ferdymercury Apr 25, 2025
89eae87
[nfc] clangformat
ferdymercury Apr 25, 2025
aa48e05
[nfc] clangf
ferdymercury Apr 25, 2025
c0c3400
[math] optimize binomial by using int instead of double as loop counter
ferdymercury Apr 25, 2025
0f5f898
[nfc] clangf
ferdymercury Apr 25, 2025
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19 changes: 11 additions & 8 deletions math/mathcore/src/TMath.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -2107,17 +2107,20 @@ Double_t TMath::BetaIncomplete(Double_t x, Double_t a, Double_t b)

////////////////////////////////////////////////////////////////////////////////
/// Calculates the binomial coefficient n over k.
/// \return the coefficient; or NaN if n < 0 or k < 0 or n < k; or 1 if k = 0 or n = k

Double_t TMath::Binomial(Int_t n,Int_t k)
Double_t TMath::Binomial(Int_t n, Int_t k)
{
if (n<0 || k<0 || n<k) return TMath::SignalingNaN();
if (k==0 || n==k) return 1;
if (n < 0 || k < 0 || n < k)
return TMath::SignalingNaN();
if (k == 0 || n == k)
return 1;

Int_t k1=TMath::Min(k,n-k);
Int_t k2=n-k1;
Double_t fact=k2+1;
for (Double_t i=k1;i>1.;--i)
fact *= (k2+i)/i;
Int_t k1 = TMath::Min(k, n - k);
auto k2 = static_cast<UInt_t>(n - k1);
Double_t fact = k2 + 1;
for (auto i = static_cast<UInt_t>(k1); i > 1; --i)
fact *= (k2 + i) / static_cast<Double_t>(i);
return fact;
}

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