void fitPol(){
int i;
TCanvas *c1=new TCanvas("c1","",200,10,700,500);
TGraph *g;

c1->Divide(2,1);
c1->cd(1);
c1->SetGrid();
Float_t x[] = {1.2, 1.1, 1.0, 0.9, 0.9, 0.8, 0.7, 0.7, 0.6, 0.5, 0.4};
int n=(sizeof(x)/sizeof(x[0]));
//Float_t y[n];
//for(i=0;i<n;i++)y[i]=0.5*x[i]**5;
Float_t y[]={1466.70,879.82,512.61,272.95,275.15,136.83,60.89,60.89,25.23,9.10,2.26};

TF1 *f =new TF1("fp","pol5",1.2,0.4);
gr=new TGraph(n,x,y);
gr->Draw("ap");
gr->SetMarkerStyle(21);
c1->cd(2);
gr->Fit(f,"R","",x[n-1],x[0]);
f->Draw("l");
}

//root [2] .x fitPol.C
//Fitting results:
//Parameters:
//NO.             VALUE           ERROR
//0       8.635926e+02    3.874606e+00
//1       -3.187407e+03   1.081146e+01
//2       2.865611e+03    7.150749e+00
//root [3] .x fitPol.C
//Fitting results:
//Parameters:
//NO.             VALUE           ERROR
//0       -6.487669e+02   1.386990e+01
//1       3.619885e+03    6.091165e+01
//2       -6.704643e+03   8.457774e+01
//3       4.249844e+03    3.742380e+01
//root [4] .x fitPol.C
//Fitting results:
//Parameters:
//NO.             VALUE           ERROR
//0       2.033629e+01    5.807645e+01
//1       -4.103278e+02   3.451078e+02
//2       1.974311e+03    7.363861e+02
//3       -3.712238e+03   6.721333e+02
//4       2.638730e+03    2.224075e+02
//root [5] .x fitPol.C
//Fitting results:
//Parameters:
//NO.             VALUE           ERROR
//0       4.474935e+02    2.436036e+02
//1       -3.654897e+03   1.829832e+03
//2       1.149710e+04    5.325322e+03
//3       -1.723937e+04   7.522046e+03
//4       1.195934e+04    5.166974e+03
//5       -2.497781e+03   1.383387e+03