// Copyright (c) 2018, ETH Zurich and UNC Chapel Hill.
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// Author: Johannes L. Schoenberger (jsch at inf.ethz.ch)

#ifndef COLMAP_SRC_OPTIM_SPRT_H_
#define COLMAP_SRC_OPTIM_SPRT_H_

#include <cmath>
#include <cstddef>
#include <vector>

namespace colmap {

// Sequential Probability Ratio Test as proposed in
//
//   "Randomized RANSAC with Sequential Probability Ratio Test",
//   Matas et al., 2005
class SPRT {
 public:
  struct Options {
    // Probability of rejecting a good model.
    double delta = 0.01;

    // A priori assumed minimum inlier ratio
    double epsilon = 0.1;

    // The ratio of the time it takes to estimate a model from a random sample
    // over the time it takes to decide whether one data sample is an
    // inlier or not. Matas et al. propose 200 for the 7-point algorithm.
    double eval_time_ratio = 200;

    // Number of models per random sample, that have to be verified. E.g. 1-3
    // for the 7-point fundamental matrix algorithm, or 1-10 for the 5-point
    // essential matrix algorithm.
    int num_models_per_sample = 1;
  };

  explicit SPRT(const Options& options);

  void Update(const Options& options);

  bool Evaluate(const std::vector<double>& residuals, const double max_residual,
                size_t* num_inliers, size_t* num_eval_samples);

 private:
  void UpdateDecisionThreshold();

  Options options_;
  double delta_epsilon_;
  double delta_1_epsilon_1_;
  double decision_threshold_;
};

}  // namespace colmap

#endif  // COLMAP_SRC_OPTIM_SPRT_H_
