Updating CDI and xAODBTaggingEfficiency with new systematic strategy

Updating CDI + xAODBTaggingEfficiency with new systematic strategy

This MR is taken as part of my qualification task in the flavour tagging group, AFT-578

What's the change?

In the current eigenvector decomposition systematic strategy (SFEigen), bin-to-bin correlations are captured for each jet-flavor in a CDI file, and reduced to a far smaller set of so-called eigenvector variations through a PCA procedure. This update enables users to perform a "global" bin-to-bin correlation across all jet-flavors simultaneously, and extract eigenvector variations that represent these correlations.

This systematic strategy can be selected in the xAODBTaggingEfficiencyTool by setting the "SystematicStrategy" property of the tool to SFGlobalEigen, for either a fixed-cut or pseudo-continuous working point.

How can we validate the method?

The SystematicStrategyComparison utility can be used with the validate_reduction function of the CalibrationEigenVariations.cxx file in order to perform these validation studies on a given (set of) CDI file(s) and working point(s). Validation studies on this method were presented in the FTAG Software Meeting here. Further documentation of the work can be found in the FTAG Documentation.