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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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16 changes: 13 additions & 3 deletions hist/hist/src/AnalyticalIntegrals.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -40,10 +40,20 @@ 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))
{
double amp = p[0];
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