How to extract Cut Value?

TMVA
1

Hi !
I’m doing some TMVA Boosted Decision Tree exercise and I’d like to save the Cut Value as a variable ? Basically the 0.019 variable. I couldn’t find the method to call.

— Factory : --------------------
— Factory : Method: Cut value:
— Factory : --------------------
— Factory : BDT: +0.019
— Factory : --------------------

Thanks !!

2

Hi,

What is it that you want to achieve with this cut value one you have it and what is your configuration to produce the given output?

Cheers,
Kim

3

I’m looping over a different choice of train and test subsamples, and would like to compute the accuracy on the results by counting the true events I get. For that I would need the cut values I guess.

The factory configurations is: factory.BookMethod(TMVA.Types.kBDT, “BDT”, "BoostType=AdaBoost:"nCuts=20:"SeparationType=GiniIndex:“Ntrees=500:MaxDepth=3”).

Thanks !

4

I’m not sure I still understand what it is you want to do. Is the cut value presented as the cut value that optimises signal efficiency * purity?

Maybe this piece of code can help you calculate the accuracy of your classifier. Basically, you can loop over the results and calculate it for a given cut value manually.

UInt_t numEvents = ...;
TMVA::Factory factory = new Factory(...);

TMVA::IMethod * imethod = factory->GetMethod("datasetName", "methodName");
TMVA::MethodBase * method = dynamic_cast<MethodBase *>(imethod);

TMVA::DataSet * dataset = method->Data();
TMVA::DataSetInfo * dsi = method->DataInfo();
TMVA::Results * results = dataset->GetResults("methodName", TMVA::Types::kTesting, TMVA::Types::kClassification);

Double_t cutValue = 0.019;
UInt_t true_positives = 0;
UInt_t false_positives = 0;
UInt_t true_negatives = 0;
UInt_t false_negatives = 0;
for (UInt_t iEvent = 0; iEvent < numEvents; ++iEvent) {
    Double_t valueEvent = results[iEvent][0];
    TMVA::Event ev = dataset->GetEvent(iEvent, TMVA::Types::kTesting);
    if (valueEvent > cutValue) {
        // Event passed cut, consider it signal
        true_positives += dsi->IsSignal(ev); // True signal
        true_positives += not (dsi->IsSignal(ev)); // True background
    } else {
        // Event failed cut, consider it background
        false_negative += dsi->IsSignal(ev); // True signal
        true_negative += not (dsi->IsSignal(ev)); // True background
    }
}

Hope this helps!

Cheers,
Kim

5

Yes, that is what I want to achieve but I need to extract the cutValue (0.019) automatically, through some
.GetCutValue -like method.

cheers, maffe.

6

Hi,

I think this is what you are looking for

TMVA::IMethod * imethod = factory->GetMethod("datasetName", "methodName");
TMVA::MethodBase * method = dynamic_cast<MethodBase *>(imethod);

Double_t cut = method->GetSignalReferenceCut();

This is what is printed when EvaluateAllMethods is run.

Cheers,
Kim

7

Marvellous Kim.
cut = GetMethod(“BDT”).GetSignalReferenceCut()
was what I was looking for.

Thanks,
maffe.

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