correctionlib 2.9.0

A generic correction library

correctionlib

Introduction

The purpose of this library is to provide a well-structured JSON data format for a wide variety of ad-hoc correction factors encountered in a typical HEP analysis and a companion evaluation tool suitable for use in C++ and python programs. Here we restrict our definition of correction factors to a class of functions with scalar inputs that produce a scalar output.

In python, the function signature is:

def f(*args: str | int | float) -> float:
    return ...

In C++, the evaluator implements this currently as:

double Correction::evaluate(const std::vector<std::variant<int, double, std::string>>& values) const;

The supported function classes include:

• multi-dimensional binned lookups;
• binned lookups pointing to multi-argument formulas with a restricted math function set (exp, sqrt, etc.);
• categorical (string or integer enumeration) maps;
• input transforms (updating one input value in place); and
• compositions of the above.

Each function type is represented by a "node" in a call graph and holds all of its parameters in a JSON structure, described by the JSON schema. Possible future extension nodes might include weigted sums (which, when composed with the others, could represent a BDT) and perhaps simple MLPs.

The tool should provide:

• standardized, versioned JSON schemas;
• forward-porting tools (to migrate data written in older schema versions); and
• a well-optimized C++ evaluator and python bindings (with numpy vectorization support).

This tool will definitely not provide:

• support for TLorentzVector or other object-type inputs (such tools should be written as a higher-level tool depending on this library as a low-level tool)

Formula support currently includes a mostly-complete subset of the ROOT library TFormula class, and is implemented in a threadsafe standalone manner. The parsing grammar is formally defined and parsed through the use of a header-only PEG parser library. The supported features mirror CMSSW's reco::formulaEvaluator and fully passes the test suite for that utility with the purposeful exception of the TMath:: namespace. The python bindings may be able to call into numexpr, though, due to the tree-like structure of the corrections, it may prove difficult to exploit vectorization at levels other than the entrypoint.

Detailed instructions for installing and using this package are provided in the documentation.

Creating new corrections

A demo/tutorial of the features is available in the documentation and also available interactively on binder

The correctionlib.schemav2 module provides a helpful framework for defining correction objects and correctionlib.convert includes select conversion routines for common types. Nodes can be type-checked as they are constructed using the parse_obj class method or by directly constructing them using keyword arguments.

Compatibility

The evaluator keys on the schema_version field in the JSON data and only operates with the same major schema version. For minor versions, the evaluator MUST remain backwards-compatible with all older minor versions of the same major series, but MAY introduce new features that make it forwards-incompatible with older readers. For patch versions, the library MUST be fully backwards-compatible and MUST NOT introduce new features or schema changes.

In practice we have not always lived up to these goals. The table below lists known deviations. Forwards-incompatible changes (marked "Forwards") are allowed under the versioning policy and are included for informational purposes only; backwards-incompatible changes (marked "Backwards") represent unintended breaks.

Version	Break type	Change
v2.2.0	Forwards (new node)	HashPRNG node added; files using it require v2.2.0+
v2.3.0	Forwards (new edge format)	UniformBinning object allowed for edges; requires v2.3.0+
v2.6.0	Forwards (new edge values)	String infinity sentinels ("inf", "-inf") allowed in edges; requires v2.6.0+
v2.6.0–v2.6.3	Backwards (patch rule violated)	Float ±inf in edges rejected with no escape hatch; files using float infinities broke. IGNORE_FLOAT_INF=True workaround added in v2.6.4
v2.7.0	Forwards (new flow value)	flow: "wrap" added to Binning/MultiBinning; requires v2.7.0+
v2.8.0	Forwards ($schema field)	"$schema" key added to JSON, rejected by older Python parsers (extra="forbid")
v2.9.0	Forwards (new node)	LWTNN node added; files using it require v2.9.0+

Developing

See CONTRIBUTING.md for details on setting up a development environment, testing, and building the documentation.