// Ceres Solver - A fast non-linear least squares minimizer

// Copyright 2015 Google Inc. All rights reserved.

// http://ceres-solver.org/

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// Author: sameeragarwal@google.com (Sameer Agarwal)

#include "ceres/ceres.h"

#include "glog/logging.h"

// f(x,y) = (1-x)^2 + 100(y - x^2)^2;

class Rosenbrock : public ceres::FirstOrderFunction {

 public:

  virtual ~Rosenbrock() {}

  virtual bool Evaluate(const double* parameters,

                        double* cost,

                        double* gradient) const {

    const double x = parameters[0];

    const double y = parameters[1];

    cost[0] = (1.0 - x) * (1.0 - x) + 100.0 * (y - x * x) * (y - x * x);

    if (gradient != NULL) {

      gradient[0] = -2.0 * (1.0 - x) - 200.0 * (y - x * x) * 2.0 * x;

      gradient[1] = 200.0 * (y - x * x);

    }

    return true;

  }

  virtual int NumParameters() const { return 2; }

};

int main(int argc, char** argv) {

  google::InitGoogleLogging(argv[0]);

  double parameters[2] = {-1.2, 1.0};

  ceres::GradientProblemSolver::Options options;

  options.minimizer_progress_to_stdout = true;

  ceres::GradientProblemSolver::Summary summary;

  ceres::GradientProblem problem(new Rosenbrock());

  ceres::Solve(options, problem, parameters, &summary);

  std::cout << summary.FullReport() << "\n";

  std::cout << "Initial x: " << -1.2 << " y: " << 1.0 << "\n";

  std::cout << "Final   x: " << parameters[0]

            << " y: " << parameters[1] << "\n";

  return 0;

}