Fitting, Integral

Hi experts.
I now want to fit pol1+gaus and pol1 respectively to the histogram. So I used the code below.

double initparms_f1[] = {1,1,5, 3.2, 6.76268e-1};
TF1 *f1 = new TF1("f1","pol1(0)+gaus(2)");
f1->FixParameter(3, 3.2);
f1->FixParameter(4, 6.76268e-1);

double initparms_f2[] = {5.59856, -1.42512e-1};
TF1 *f2 = new TF1("f2","pol1");
f2->FixParameter(0, 5.59856);
f2->FixParameter(1, -1.42512e-1);

auto fitresult1 = N_37->Fit(f1,"S","",1,20);
auto fitresult2 = N_37->Fit(f2,"S+","",1,20);

double integral1 = f1->Integral(1,20);
double integral2 = f2->Integral(1,20);

auto covMatrix1 = fitresult1->GetCovarianceMatrix();
auto covMatrix2 = fitresult2->GetCovarianceMatrix();

double sigma_integral1 = f1->IntegralError(1,20,fitresult1->GetParams(),covMatrix1.GetMatrixArray());
double sigma_integral2 = f2->IntegralError(1,20,fitresult2->GetParams(),covMatrix2.GetMatrixArray());

std::cout << "Number of signal event = " << 2*integral1-2*integral2 << "+/-" << 2*sigma_integral1-2*sigma_integral2 << std::endl;

However, I want to apply the parameters of pol1 obtained from f1(pol1+gaus) as initial parameters to pol1 of f2(pol1).

And also can i get integral error different way?

Thanks for reply! But I can’t find about parameter information.

This example shows how to get the fit parameters. May be that’s what you need.

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