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

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

//

// Detailed descriptions of these preconditions beyond what is

// documented here can be found in

//

// Bundle Adjustment in the Large

// S. Agarwal, N. Snavely, S. Seitz & R. Szeliski, ECCV 2010

// http://www.cs.washington.edu/homes/sagarwal/bal.pdf

#ifndef CERES_INTERNAL_SCHUR_JACOBI_PRECONDITIONER_H_

#define CERES_INTERNAL_SCHUR_JACOBI_PRECONDITIONER_H_

#include <set>

#include <vector>

#include <utility>

#include "ceres/collections_port.h"

#include "ceres/internal/macros.h"

#include "ceres/internal/scoped_ptr.h"

#include "ceres/preconditioner.h"

namespace ceres {

namespace internal {

class BlockRandomAccessDiagonalMatrix;

class BlockSparseMatrix;

struct CompressedRowBlockStructure;

class SchurEliminatorBase;

// This class implements the SCHUR_JACOBI preconditioner for Structure

// from Motion/Bundle Adjustment problems. Full mathematical details

// can be found in

//

// Bundle Adjustment in the Large

// S. Agarwal, N. Snavely, S. Seitz & R. Szeliski, ECCV 2010

// http://www.cs.washington.edu/homes/sagarwal/bal.pdf

//

// Example usage:

//

//   Preconditioner::Options options;

//   options.preconditioner_type = SCHUR_JACOBI;

//   options.elimination_groups.push_back(num_points);

//   options.elimination_groups.push_back(num_cameras);

//   SchurJacobiPreconditioner preconditioner(

//      *A.block_structure(), options);

//   preconditioner.Update(A, NULL);

//   preconditioner.RightMultiply(x, y);

//

class SchurJacobiPreconditioner : public BlockSparseMatrixPreconditioner {

 public:

  // Initialize the symbolic structure of the preconditioner. bs is

  // the block structure of the linear system to be solved. It is used

  // to determine the sparsity structure of the preconditioner matrix.

  //

  // It has the same structural requirement as other Schur complement

  // based solvers. Please see schur_eliminator.h for more details.

  SchurJacobiPreconditioner(const CompressedRowBlockStructure& bs,

                            const Preconditioner::Options& options);

  virtual ~SchurJacobiPreconditioner();

  // Preconditioner interface.

  virtual void RightMultiply(const double* x, double* y) const;

  virtual int num_rows() const;

 private:

  void InitEliminator(const CompressedRowBlockStructure& bs);

  virtual bool UpdateImpl(const BlockSparseMatrix& A, const double* D);

  Preconditioner::Options options_;

  scoped_ptr<SchurEliminatorBase> eliminator_;

  // Preconditioner matrix.

  scoped_ptr<BlockRandomAccessDiagonalMatrix> m_;

  CERES_DISALLOW_COPY_AND_ASSIGN(SchurJacobiPreconditioner);

};

}  // namespace internal

}  // namespace ceres

#endif  // CERES_INTERNAL_SCHUR_JACOBI_PRECONDITIONER_H_