Save user defined function to a file

ROOT
1

Hi,

I have a problem with saving my own fitting function to a ROOT file: saved fuction does not respond to changing its parameters. Here is a short example:

testF1() {
    TCanvas *c1 = new TCanvas("c1", "", -1);
    c1->Divide(1,2);
    c1->cd(1);
    TF1 *f1 = new TF1("f1", N, 0, 10, 1);
    f1->SetParameter(0, 0);
    f1->Draw(); // all OK: y=sin(x)

    TFile out("testF1.root", "recreate");
    f1->Write();
    out.Close();

    c1->cd(2);
    TFile in("testF1.root");
    TF1 *f2 = (TF1*)in.Get("f1");
    f2->SetParameter(0, 1); // has no effect!
    f2->Draw(); // here is a problem: I get y=sin(x)+0 instead of y=sin(x)+1
    in.Close();
}

Double_t N(Double_t *x, Double_t *par) {
    return sin(x[0]) + par[0];
}

How do I save the function correctly to be able to change is’s parameters and get suitable answer?

2

CINT interpreted functions or compiled functions are not saved
to the root file. ROOT saves only the result of the function
at fNpx points such that these functions can still be visualized.
Only functions with inline expressions are saved.
In your case, replace the interpreted function by

TF1 *f1 = new TF1(“f1”, “sin(x)+[0]”, 0, 10);

Rene