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

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

#include "ceres/schur_jacobi_preconditioner.h"

#include <utility>

#include <vector>

#include "ceres/block_random_access_diagonal_matrix.h"

#include "ceres/block_sparse_matrix.h"

#include "ceres/collections_port.h"

#include "ceres/internal/scoped_ptr.h"

#include "ceres/linear_solver.h"

#include "ceres/schur_eliminator.h"

#include "glog/logging.h"

namespace ceres {

namespace internal {

SchurJacobiPreconditioner::SchurJacobiPreconditioner(

    const CompressedRowBlockStructure& bs,

    const Preconditioner::Options& options)

    : options_(options) {

  CHECK_GT(options_.elimination_groups.size(), 1);

  CHECK_GT(options_.elimination_groups[0], 0);

  const int num_blocks = bs.cols.size() - options_.elimination_groups[0];

  CHECK_GT(num_blocks, 0)

      << "Jacobian should have atleast 1 f_block for "

      << "SCHUR_JACOBI preconditioner.";

  std::vector<int> blocks(num_blocks);

  for (int i = 0; i < num_blocks; ++i) {

    blocks[i] = bs.cols[i + options_.elimination_groups[0]].size;

  }

  m_.reset(new BlockRandomAccessDiagonalMatrix(blocks));

  InitEliminator(bs);

}

SchurJacobiPreconditioner::~SchurJacobiPreconditioner() {

}

// Initialize the SchurEliminator.

void SchurJacobiPreconditioner::InitEliminator(

    const CompressedRowBlockStructure& bs) {

  LinearSolver::Options eliminator_options;

  eliminator_options.elimination_groups = options_.elimination_groups;

  eliminator_options.num_threads = options_.num_threads;

  eliminator_options.e_block_size = options_.e_block_size;

  eliminator_options.f_block_size = options_.f_block_size;

  eliminator_options.row_block_size = options_.row_block_size;

  eliminator_.reset(SchurEliminatorBase::Create(eliminator_options));

  const bool kFullRankETE = true;

  eliminator_->Init(

      eliminator_options.elimination_groups[0], kFullRankETE, &bs);

}

// Update the values of the preconditioner matrix and factorize it.

bool SchurJacobiPreconditioner::UpdateImpl(const BlockSparseMatrix& A,

                                           const double* D) {

  const int num_rows = m_->num_rows();

  CHECK_GT(num_rows, 0);

  // We need a dummy rhs vector and a dummy b vector since the Schur

  // eliminator combines the computation of the reduced camera matrix

  // with the computation of the right hand side of that linear

  // system.

  //

  // TODO(sameeragarwal): Perhaps its worth refactoring the

  // SchurEliminator::Eliminate function to allow NULL for the rhs. As

  // of now it does not seem to be worth the effort.

  Vector rhs = Vector::Zero(m_->num_rows());

  Vector b = Vector::Zero(A.num_rows());

  // Compute a subset of the entries of the Schur complement.

  eliminator_->Eliminate(&A, b.data(), D, m_.get(), rhs.data());

  m_->Invert();

  return true;

}

void SchurJacobiPreconditioner::RightMultiply(const double* x,

                                              double* y) const {

  m_->RightMultiply(x, y);

}

int SchurJacobiPreconditioner::num_rows() const {

  return m_->num_rows();

}

}  // namespace internal

}  // namespace ceres