// Ceres Solver - A fast non-linear least squares minimizer
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// http://ceres-solver.org/
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// Author: sameeragarwal@google.com (Sameer Agarwal)

#include <limits>

#include "ceres/ceres.h"
#include "gtest/gtest.h"

namespace ceres::internal {

class QuadraticFirstOrderFunction : public ceres::FirstOrderFunction {
 public:
  bool Evaluate(const double* parameters,
                double* cost,
                double* gradient) const final {
    cost[0] = parameters[0] * parameters[0];
    if (gradient != nullptr) {
      gradient[0] = 2.0 * parameters[0];
    }
    return true;
  }

  int NumParameters() const final { return 1; }
};

TEST(LineSearchMinimizerTest, FinalCostIsZero) {
  double parameters[1] = {2.0};
  ceres::GradientProblem problem(new QuadraticFirstOrderFunction);
  ceres::GradientProblemSolver::Options options;
  ceres::GradientProblemSolver::Summary summary;
  ceres::Solve(options, problem, parameters, &summary);
  EXPECT_NEAR(summary.final_cost, 0.0, std::numeric_limits<double>::epsilon());
}

}  // namespace ceres::internal