[hist] Using TKDE::Fill works with empty tkde

[aaronj0]

This PR fixes

• https://github.com/root-project/root/issues/7808

This is happening because in when the parentheses operator overload TKDE::operator()(Double_t x) calls ReInit (const_cast<TKDE*>(this))->ReInit() it returns before setting the fKernel in the case of new data.

One approach is to call SetKernel here:

if (fNewData)  {
      InitFromNewData();
      SetKernel();
      return;
   }

or call it at the end of InitFromNewData().

When that happens, the fKernel is no longer null but this error is reproducible with both iterative options - With Adaptive we get NaN and Fixed we get inf

This is because the weight calculation is using the nSum that is 0 when binning is not used Inversing that gives the infinity in the Iteration:Fixed case

This fix:

• adds the call to SetBinCountData() in InitFromNewData()
• recreates the kernel fun pointer (previously fKernel ends up a nullptr)
• calculating nSum as fNEvents if not binning in TKDE::TKernel::operator().

Results:

    auto kde = new TKDE(0, nullptr, 0, 5, "KernelType:Gaussian;Iteration:Adaptive;Mirror:noMirror;Binning:RelaxedBinning", 1);
    for (unsigned int i = 0; i < 100; i++) { kde->Fill(gRandom->Gaus(2,1)); }
    std::cout<<kde->GetValue(2)<<"\n"; 

Gives 0.487581

[phsft-bot]

Can one of the admins verify this patch?

[lmoneta]

@phsft-bot build

[phsft-bot]

Starting build on ROOT-performance-centos8-multicore/soversion, ROOT-ubuntu2204/nortcxxmod, ROOT-ubuntu2004/python3, mac12arm/cxx20, windows10/default How to customize builds

[phsft-bot]

Build failed on ROOT-ubuntu2004/python3. See console output.

[phsft-bot]

Build failed on ROOT-ubuntu2204/nortcxxmod. Running on root-ubuntu-2204-2.cern.ch:/home/sftnight/build/workspace/root-pullrequests-build See console output.

Failing tests:

• projectroot.hist.hist.test.gtest_hist_hist_test_testTKDE

[phsft-bot]

Build failed on windows10/default. Running on null:C:\build\workspace\root-pullrequests-build See console output.

Failing tests:

• projectroot.hist.hist.test.gtest_hist_hist_test_testTKDE

[phsft-bot]

Build failed on ROOT-performance-centos8-multicore/soversion. Running on olbdw-01.cern.ch:/data/sftnight/workspace/root-pullrequests-build See console output.

Failing tests:

• projectroot.hist.hist.test.gtest_hist_hist_test_testTKDE

[phsft-bot]

Build failed on mac12arm/cxx20. Running on 194.12.161.128:/Users/sftnight/build/workspace/root-pullrequests-build See console output.

Failing tests:

• projectroot.hist.hist.test.gtest_hist_hist_test_testTKDE

[github-actions[bot]]

Test Results

    12 files      12 suites   2d 5h 22m 15s :stopwatch:  2 561 tests  2 559 :white_check_mark: 0 :zzz:  2 :x: 28 810 runs  28 796 :white_check_mark: 0 :zzz: 14 :x:

For more details on these failures, see this check.

Results for commit e8707bd9.