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

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

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// Author: keir@google.com (Keir Mierle)

#ifndef CERES_INTERNAL_BLOCK_JACOBI_PRECONDITIONER_H_

#define CERES_INTERNAL_BLOCK_JACOBI_PRECONDITIONER_H_

#include "ceres/block_random_access_diagonal_matrix.h"

#include "ceres/internal/scoped_ptr.h"

#include "ceres/preconditioner.h"

namespace ceres {

namespace internal {

class BlockSparseMatrix;

struct CompressedRowBlockStructure;

// A block Jacobi preconditioner. This is intended for use with

// conjugate gradients, or other iterative symmetric solvers. To use

// the preconditioner, create one by passing a BlockSparseMatrix "A"

// to the constructor. This fixes the sparsity pattern to the pattern

// of the matrix A^TA.

//

// Before each use of the preconditioner in a solve with conjugate gradients,

// update the matrix by running Update(A, D). The values of the matrix A are

// inspected to construct the preconditioner. The vector D is applied as the

// D^TD diagonal term.

class BlockJacobiPreconditioner : public BlockSparseMatrixPreconditioner {

 public:

  // A must remain valid while the BlockJacobiPreconditioner is.

  explicit BlockJacobiPreconditioner(const BlockSparseMatrix& A);

  virtual ~BlockJacobiPreconditioner();

  // Preconditioner interface

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

  virtual int num_rows() const { return m_->num_rows(); }

  virtual int num_cols() const { return m_->num_rows(); }

  const BlockRandomAccessDiagonalMatrix& matrix() const { return *m_; }

 private:

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

  scoped_ptr<BlockRandomAccessDiagonalMatrix> m_;

};

}  // namespace internal

}  // namespace ceres

#endif  // CERES_INTERNAL_BLOCK_JACOBI_PRECONDITIONER_H_