ActsPlugins/Root/RootHistogramFit.hpp

0001 // This file is part of the ACTS project.
0002 //
0003 // Copyright (C) 2016 CERN for the benefit of the ACTS project
0004 //
0005 // This Source Code Form is subject to the terms of the Mozilla Public
0006 // License, v. 2.0. If a copy of the MPL was not distributed with this
0007 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
0008
0009 #pragma once
0010
0011 #include "Acts/Utilities/Histogram.hpp"
0012
0013 #include <optional>
0014 #include <string>
0015 #include <tuple>
0016 #include <utility>
0017
0018 namespace ActsPlugins {
0019
0020 /// Fit a Gaussian to a histogram via ROOT's `TH1::Fit`
0021 ///
0022 /// `operator()`'s signature matches `ActsExamples::HistogramFitFunction`
0023 /// exactly, so a `RootHistogramFit` instance can be used directly as one with
0024 /// no adapter.
0025 class RootHistogramFit {
0026  public:
0027   /// Configuration for @c RootHistogramFit
0028   struct Config {
0029     /// `TH1::Fit` option string. Must keep `"S"` (return a `TFitResult`) and
0030     /// `"0"` (do not draw); the ranged fit adds `"R"` itself. Defaults to
0031     /// ROOT's least-squares fit; use `"LSQ0"` for the likelihood fit instead.
0032     std::string fitOptions = "SQ0";
0033   };
0034
0035   /// Outcome of the fit: `(mean, sigma, meanError, sigmaError)`
0036   using Result = std::tuple<double, double, double, double>;
0037   /// Fit range `[xMin, xMax]`, closed, selected by bin centre
0038   using Range = std::pair<double, double>;
0039
0040   RootHistogramFit() = default;
0041
0042   /// Construct with the given configuration
0043   /// @param config The fit configuration
0044   explicit RootHistogramFit(Config config) : m_config(std::move(config)) {}
0045
0046   /// The fit configuration
0047   /// @return The configuration this instance was constructed with
0048   const Config& config() const { return m_config; }
0049
0050   /// Fit a Gaussian to a histogram, optionally restricted to a range
0051   ///
0052   /// @param hist The histogram to fit
0053   /// @param range If set, only bins whose centre lies in `[range->first,
0054   ///              range->second]` enter the fit
0055   /// @return `(mean, sigma, meanError, sigmaError)`, or `std::nullopt` if the
0056   ///         fit could not be performed
0057   std::optional<Result> operator()(
0058       const Acts::Experimental::Histogram1& hist,
0059       std::optional<Range> range = std::nullopt) const;
0060
0061  private:
0062   Config m_config{};
0063 };
0064
0065 }  // namespace ActsPlugins