Memory management with many TGraph.Fit()

Newbie
1

I have a pseudocode which looks like this

double fitFunc(...){
    vector<double> x, y, x_err, y_err;
    // fill vectors
    if(x.size() <= 1) return 0;

    TGraphErrors gr(x.size(), &x[0], &y[0], &x_err[0], &y_err[0]);
    gr.Fit("pol1", "Q");
    TF1 fit = *gr.GetFunction("pol1");

    // Adding this part makes code `killed` after 100k events
    for(int j=0; j < n_refits; ++j){
        int idx = // pick some bad idx to throw away;
        x.erase(x.begin() + idx);
        // ...
        if(x.size() <= 1) return 0;

        gr = TGraphErrors(x.size(), &x[0], &y[0], &x_err[0], &y_err[0]);
        gr.Fit("pol1", "Q");
        fit = *gr.GetFunction("pol1");
    }
    return fit.GetParameter(0);
}

The function is called for each event inside with RDataFrame

Process gets killed after 100k events, which doesn’t happen with n_refits = 0.
Because of that I think refit part of the code is very bad…

I am not good at mem leakages and this is probably basic C++ question
Is there obvious mistake I am missing? Or how to improve this part of the code?

cheers

ROOT Version: master
Platform: Centos 7
Compiler: gcc 10

2

I can reproduce it, working on a fix for a future ROOT version. Until then, this should do as a workaround:

double fitFunc(...) {
    vector<double> x, y, x_err, y_err;
    // fill vectors
    if(x.size() <= 1) return 0;

    double ret = 0;
    TGraphErrors gr(x.size(), &x[0], &y[0], &x_err[0], &y_err[0]);
    gr.Fit("pol1", "Q");
    double ret = gr.GetFunction("pol1")->GetParameter(0);

    // Adding this part makes code `killed` after 100k events
    for(int j=0; j < n_refits; ++j){
        int idx = // pick some bad idx to throw away;
        x.erase(x.begin() + idx);
        // ...
        if(x.size() <= 1) return 0;

        TGraphErrors grRefit(x.size(), &x[0], &y[0], &x_err[0], &y_err[0]);
        grRefit.Fit("pol1", "Q");
        ret = grRefit.GetFunction("pol1")->GetParameter(0);
    }
    return ret;
}
1 Like
3

It’s a leak in fit = *gr.GetFunction("pol1"); (TF1::Copy() to be precise.) @moneta offered to provide a fix - thanks, Lorenzo!

@FoxWise thank you for reporting this!

1 Like