// 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)

#ifndef CERES_INTERNAL_COORDINATE_DESCENT_MINIMIZER_H_

#define CERES_INTERNAL_COORDINATE_DESCENT_MINIMIZER_H_

#include <string>

#include <vector>

#include "ceres/evaluator.h"

#include "ceres/minimizer.h"

#include "ceres/problem_impl.h"

#include "ceres/solver.h"

namespace ceres {

namespace internal {

class Program;

class LinearSolver;

// Given a Program, and a ParameterBlockOrdering which partitions

// (non-exhaustively) the Hessian matrix into independent sets,

// perform coordinate descent on the parameter blocks in the

// ordering. The independent set structure allows for all parameter

// blocks in the same independent set to be optimized in parallel, and

// the order of the independent set determines the order in which the

// parameter block groups are optimized.

//

// The minimizer assumes that none of the parameter blocks in the

// program are constant.

class CoordinateDescentMinimizer : public Minimizer {

 public:

  bool Init(const Program& program,

            const ProblemImpl::ParameterMap& parameter_map,

            const ParameterBlockOrdering& ordering,

            std::string* error);

  // Minimizer interface.

  virtual ~CoordinateDescentMinimizer();

  virtual void Minimize(const Minimizer::Options& options,

                        double* parameters,

                        Solver::Summary* summary);

  // Verify that each group in the ordering forms an independent set.

  static bool IsOrderingValid(const Program& program,

                              const ParameterBlockOrdering& ordering,

                              std::string* message);

  // Find a recursive decomposition of the Hessian matrix as a set

  // of independent sets of decreasing size and invert it. This

  // seems to work better in practice, i.e., Cameras before

  // points.

  static ParameterBlockOrdering* CreateOrdering(const Program& program);

 private:

  void Solve(Program* program,

             LinearSolver* linear_solver,

             double* parameters,

             Solver::Summary* summary);

  std::vector<ParameterBlock*> parameter_blocks_;

  std::vector<std::vector<ResidualBlock*> > residual_blocks_;

  // The optimization is performed in rounds. In each round all the

  // parameter blocks that form one independent set are optimized in

  // parallel. This array, marks the boundaries of the independent

  // sets in parameter_blocks_.

  std::vector<int> independent_set_offsets_;

  Evaluator::Options evaluator_options_;

};

}  // namespace internal

}  // namespace ceres

#endif  // CERES_INTERNAL_COORDINATE_DESCENT_MINIMIZER_H_