How to get covariance matrix

ROOT
1

Dear Root users,

I would like to get the covariance matrix from my fit, but I don’t know how to do it. Could you please indicate me? I tried like below, but it did not work.

Thank you very much,

int QA2() { Double_t x[]={1,2,3,4,5}; Double_t y[]={1.1, 1.9, 3.2, 3.9, 5.5}; TGraph *g = new TGraph(5,x,y); g->Draw("A*P"); TFitResult *kq = g->Fit("pol1"); kq.CovMatrix(); return 0; }

2

See “Access to the fit result” in the TGraph::Fit method description.

[code]#include “TGraph.h”
#include “TFitResult.h”
#include “TMatrixD.h”

int QA2()
{
Double_t x[] = {1, 2, 3, 4, 5};
Double_t y[] = {1.1, 1.9, 3.2, 3.9, 5.5};
TGraph g = new TGraph((sizeof(x) / sizeof(Double_t)), x, y);
g->Draw("A");
TFitResultPtr r = g->Fit(“pol1”, “S”);
TMatrixD cov = r->GetCorrelationMatrix();
TMatrixD cor = r->GetCovarianceMatrix();
cov.Print();
cor.Print();
return 0;
}[/code]