// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2012 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
//
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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 <vector>
#include "ceres/preconditioner.h"

namespace ceres {
namespace internal {

class BlockSparseMatrix;
struct CompressedRowBlockStructure;
class LinearOperator;

// 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 void LeftMultiply(const double* x, double* y) const;
  virtual int num_rows() const { return num_rows_; }
  virtual int num_cols() const { return num_rows_; }

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

  std::vector<double*> blocks_;
  std::vector<double> block_storage_;
  int num_rows_;

  // The block structure of the matrix this preconditioner is for (e.g. J).
  const CompressedRowBlockStructure& block_structure_;
};

}  // namespace internal
}  // namespace ceres

#endif  // CERES_INTERNAL_BLOCK_JACOBI_PRECONDITIONER_H_