// Ceres Solver - A fast non-linear least squares minimizer
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// http://ceres-solver.org/
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// Author: markshachkov@gmail.com (Mark Shachkov)

#ifndef CERES_INTERNAL_POWER_SERIES_EXPANSION_PRECONDITIONER_H_
#define CERES_INTERNAL_POWER_SERIES_EXPANSION_PRECONDITIONER_H_

#include "ceres/implicit_schur_complement.h"
#include "ceres/internal/eigen.h"
#include "ceres/internal/export.h"
#include "ceres/preconditioner.h"

namespace ceres::internal {

// This is a preconditioner via power series expansion of Schur
// complement inverse based on "Weber et al, Power Bundle Adjustment for
// Large-Scale 3D Reconstruction".
//
//
// TODO(https://github.com/ceres-solver/ceres-solver/issues/934): In
// PowerSeriesExpansionPreconditioner::RightMultiplyAndAccumulate only
// operations performed via ImplicitSchurComplement are threaded.
// PowerSeriesExpansionPreconditioner will benefit from multithreading
// applied to remaning operations (block-sparse right product and several
// vector operations)
class CERES_NO_EXPORT PowerSeriesExpansionPreconditioner
    : public Preconditioner {
 public:
  PowerSeriesExpansionPreconditioner(const ImplicitSchurComplement* isc,
                                     const int max_num_spse_iterations,
                                     const double spse_tolerance);
  PowerSeriesExpansionPreconditioner(
      const PowerSeriesExpansionPreconditioner&) = delete;
  void operator=(const PowerSeriesExpansionPreconditioner&) = delete;
  ~PowerSeriesExpansionPreconditioner() override;

  void RightMultiplyAndAccumulate(const double* x, double* y) const final;
  bool Update(const LinearOperator& A, const double* D) final;
  int num_rows() const final;

 private:
  const ImplicitSchurComplement* isc_;
  const int max_num_spse_iterations_;
  const double spse_tolerance_;
};

}  // namespace ceres::internal

#endif  // CERES_INTERNAL_POWER_SERIES_EXPANSION_PRECONDITIONER_H_