// Ceres Solver - A fast non-linear least squares minimizer
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// Author: keir@google.com (Keir Mierle)

#include "ceres/block_jacobi_preconditioner.h"

#include "ceres/block_random_access_diagonal_matrix.h"
#include "ceres/block_sparse_matrix.h"
#include "ceres/block_structure.h"
#include "ceres/casts.h"
#include "ceres/internal/eigen.h"

namespace ceres::internal {

BlockJacobiPreconditioner::BlockJacobiPreconditioner(
    const BlockSparseMatrix& A) {
  const CompressedRowBlockStructure* bs = A.block_structure();
  std::vector<int> blocks(bs->cols.size());
  for (int i = 0; i < blocks.size(); ++i) {
    blocks[i] = bs->cols[i].size;
  }

  m_ = std::make_unique<BlockRandomAccessDiagonalMatrix>(blocks);
}

BlockJacobiPreconditioner::~BlockJacobiPreconditioner() = default;

bool BlockJacobiPreconditioner::UpdateImpl(const BlockSparseMatrix& A,
                                           const double* D) {
  const CompressedRowBlockStructure* bs = A.block_structure();
  const double* values = A.values();
  m_->SetZero();
  for (int i = 0; i < bs->rows.size(); ++i) {
    const int row_block_size = bs->rows[i].block.size;
    const std::vector<Cell>& cells = bs->rows[i].cells;
    for (const auto& cell : cells) {
      const int block_id = cell.block_id;
      const int col_block_size = bs->cols[block_id].size;

      int r, c, row_stride, col_stride;
      CellInfo* cell_info =
          m_->GetCell(block_id, block_id, &r, &c, &row_stride, &col_stride);
      MatrixRef m(cell_info->values, row_stride, col_stride);
      ConstMatrixRef b(values + cell.position, row_block_size, col_block_size);
      m.block(r, c, col_block_size, col_block_size) += b.transpose() * b;
    }
  }

  if (D != nullptr) {
    // Add the diagonal.
    int position = 0;
    for (int i = 0; i < bs->cols.size(); ++i) {
      const int block_size = bs->cols[i].size;
      int r, c, row_stride, col_stride;
      CellInfo* cell_info = m_->GetCell(i, i, &r, &c, &row_stride, &col_stride);
      MatrixRef m(cell_info->values, row_stride, col_stride);
      m.block(r, c, block_size, block_size).diagonal() +=
          ConstVectorRef(D + position, block_size).array().square().matrix();
      position += block_size;
    }
  }

  m_->Invert();
  return true;
}

void BlockJacobiPreconditioner::RightMultiply(const double* x,
                                              double* y) const {
  m_->RightMultiply(x, y);
}

}  // namespace ceres::internal