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Fix edge case in analytical integral of exponential TF1 #20992

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Fix edge case in analytical integral of exponential TF1 #20992

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71c399b
Fix edge case in analytical integral of exponential TF1
swetank18 Jan 23, 2026
319674f
Apply clang-format
swetank18 Jan 28, 2026
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29 changes: 18 additions & 11 deletions hist/hist/src/AnalyticalIntegrals.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -40,11 +40,21 @@ Double_t AnalyticalIntegral(TF1 *f, Double_t a, Double_t b)
return TMath::QuietNaN();
}

if (num == 200)//expo: exp(p0+p1*x)
{
result = ( exp(p[0]+p[1]*xmax) - exp(p[0]+p[1]*xmin))/p[1];
else if (num == 200) { // expo: exp(p0 + p1*x)
const double p0 = p[0];
const double p1 = p[1];

if (p1 == 0) {
// Limit p1 -> 0: integral of constant exp(p0)
result = std::exp(p0) * (xmax - xmin);
} else {
const double ea = p0 + p1 * xmin;
const double eb = p0 + p1 * xmax;
result = (std::exp(eb) - std::exp(ea)) / p1;
}
}
else if (num == 100)//gaus: [0]*exp(-0.5*((x-[1])/[2])^2))

else if (num == 100) // gaus: [0]*exp(-0.5*((x-[1])/[2])^2))
{
double amp = p[0];
double mean = p[1];
Expand All @@ -54,8 +64,7 @@ Double_t AnalyticalIntegral(TF1 *f, Double_t a, Double_t b)
else
result = amp * sqrt(2 * TMath::Pi()) * sigma *
(ROOT::Math::gaussian_cdf(xmax, sigma, mean) - ROOT::Math::gaussian_cdf(xmin, sigma, mean)); //
}
else if (num == 400)//landau: root::math::landau(x,mpv=0,sigma=1,bool norm=false)
} else if (num == 400) // landau: root::math::landau(x,mpv=0,sigma=1,bool norm=false)
{

double amp = p[0];
Expand All @@ -66,8 +75,7 @@ Double_t AnalyticalIntegral(TF1 *f, Double_t a, Double_t b)
result = amp*(ROOT::Math::landau_cdf(xmax,sigma,mean) - ROOT::Math::landau_cdf(xmin,sigma,mean));
else
result = amp*sigma*(ROOT::Math::landau_cdf(xmax,sigma,mean) - ROOT::Math::landau_cdf(xmin,sigma,mean));
}
else if (num == 500) //crystal ball
} else if (num == 500) // crystal ball
{
double amp = p[0];
double mean = p[1];
Expand All @@ -83,15 +91,14 @@ Double_t AnalyticalIntegral(TF1 *f, Double_t a, Double_t b)
}
}

else if (num >= 300 && num < 400)//polN
else if (num >= 300 && num < 400) // polN
{
Int_t n = num - 300;
for (int i=0;i<n+1;i++)
{
result += p[i]/(i+1)*(std::pow(xmax,i+1)-std::pow(xmin,i+1));
}
}
else
} else
result = TMath::QuietNaN();

return result;
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