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diff --git a/internal/ceres/visibility_based_preconditioner_test.cc b/internal/ceres/visibility_based_preconditioner_test.cc
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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2015 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameeragarwal@google.com (Sameer Agarwal)
+
+#include "ceres/visibility_based_preconditioner.h"
+
+#include <memory>
+#include "Eigen/Dense"
+#include "ceres/block_random_access_dense_matrix.h"
+#include "ceres/block_random_access_sparse_matrix.h"
+#include "ceres/block_sparse_matrix.h"
+#include "ceres/casts.h"
+#include "ceres/file.h"
+#include "ceres/internal/eigen.h"
+#include "ceres/linear_least_squares_problems.h"
+#include "ceres/schur_eliminator.h"
+#include "ceres/stringprintf.h"
+#include "ceres/test_util.h"
+#include "ceres/types.h"
+#include "glog/logging.h"
+#include "gtest/gtest.h"
+
+namespace ceres {
+namespace internal {
+
+// TODO(sameeragarwal): Re-enable this test once serialization is
+// working again.
+
+// using testing::AssertionResult;
+// using testing::AssertionSuccess;
+// using testing::AssertionFailure;
+
+// static const double kTolerance = 1e-12;
+
+// class VisibilityBasedPreconditionerTest : public ::testing::Test {
+//  public:
+//   static const int kCameraSize = 9;
+
+//  protected:
+//   void SetUp() {
+//     string input_file = TestFileAbsolutePath("problem-6-1384-000.lsqp");
+
+//     std::unique_ptr<LinearLeastSquaresProblem> problem(
+//         CHECK_NOTNULL(CreateLinearLeastSquaresProblemFromFile(input_file)));
+//     A_.reset(down_cast<BlockSparseMatrix*>(problem->A.release()));
+//     b_.reset(problem->b.release());
+//     D_.reset(problem->D.release());
+
+//     const CompressedRowBlockStructure* bs =
+//         CHECK_NOTNULL(A_->block_structure());
+//     const int num_col_blocks = bs->cols.size();
+
+//     num_cols_ = A_->num_cols();
+//     num_rows_ = A_->num_rows();
+//     num_eliminate_blocks_ = problem->num_eliminate_blocks;
+//     num_camera_blocks_ = num_col_blocks - num_eliminate_blocks_;
+//     options_.elimination_groups.push_back(num_eliminate_blocks_);
+//     options_.elimination_groups.push_back(
+//         A_->block_structure()->cols.size() - num_eliminate_blocks_);
+
+//     vector<int> blocks(num_col_blocks - num_eliminate_blocks_, 0);
+//     for (int i = num_eliminate_blocks_; i < num_col_blocks; ++i) {
+//       blocks[i - num_eliminate_blocks_] = bs->cols[i].size;
+//     }
+
+//     // The input matrix is a real jacobian and fairly poorly
+//     // conditioned. Setting D to a large constant makes the normal
+//     // equations better conditioned and makes the tests below better
+//     // conditioned.
+//     VectorRef(D_.get(), num_cols_).setConstant(10.0);
+
+//     schur_complement_.reset(new BlockRandomAccessDenseMatrix(blocks));
+//     Vector rhs(schur_complement_->num_rows());
+
+//     std::unique_ptr<SchurEliminatorBase> eliminator;
+//     LinearSolver::Options eliminator_options;
+//     eliminator_options.elimination_groups = options_.elimination_groups;
+//     eliminator_options.num_threads = options_.num_threads;
+
+//     eliminator.reset(SchurEliminatorBase::Create(eliminator_options));
+//     eliminator->Init(num_eliminate_blocks_, bs);
+//     eliminator->Eliminate(A_.get(), b_.get(), D_.get(),
+//                           schur_complement_.get(), rhs.data());
+//   }
+
+//   AssertionResult IsSparsityStructureValid() {
+//     preconditioner_->InitStorage(*A_->block_structure());
+//     const std::unordered_set<pair<int, int>, pair_hash>& cluster_pairs =
+//     get_cluster_pairs(); const vector<int>& cluster_membership =
+//     get_cluster_membership();
+
+//     for (int i = 0; i < num_camera_blocks_; ++i) {
+//       for (int j = i; j < num_camera_blocks_; ++j) {
+//         if (cluster_pairs.count(make_pair(cluster_membership[i],
+//                                           cluster_membership[j]))) {
+//           if (!IsBlockPairInPreconditioner(i, j)) {
+//             return AssertionFailure()
+//                 << "block pair (" << i << "," << j << "missing";
+//           }
+//         } else {
+//           if (IsBlockPairInPreconditioner(i, j)) {
+//             return AssertionFailure()
+//                << "block pair (" << i << "," << j << "should not be present";
+//           }
+//         }
+//       }
+//     }
+//     return AssertionSuccess();
+//   }
+
+//   AssertionResult PreconditionerValuesMatch() {
+//     preconditioner_->Update(*A_, D_.get());
+//     const std::unordered_set<pair<int, int>, pair_hash>& cluster_pairs =
+//     get_cluster_pairs(); const BlockRandomAccessSparseMatrix* m = get_m();
+//     Matrix preconditioner_matrix;
+//     m->matrix()->ToDenseMatrix(&preconditioner_matrix);
+//     ConstMatrixRef full_schur_complement(schur_complement_->values(),
+//                                          m->num_rows(),
+//                                          m->num_rows());
+//     const int num_clusters = get_num_clusters();
+//     const int kDiagonalBlockSize =
+//         kCameraSize * num_camera_blocks_ / num_clusters;
+
+//     for (int i = 0; i < num_clusters; ++i) {
+//       for (int j = i; j < num_clusters; ++j) {
+//         double diff = 0.0;
+//         if (cluster_pairs.count(make_pair(i, j))) {
+//           diff =
+//               (preconditioner_matrix.block(kDiagonalBlockSize * i,
+//                                            kDiagonalBlockSize * j,
+//                                            kDiagonalBlockSize,
+//                                            kDiagonalBlockSize) -
+//                full_schur_complement.block(kDiagonalBlockSize * i,
+//                                            kDiagonalBlockSize * j,
+//                                            kDiagonalBlockSize,
+//                                            kDiagonalBlockSize)).norm();
+//         } else {
+//           diff = preconditioner_matrix.block(kDiagonalBlockSize * i,
+//                                              kDiagonalBlockSize * j,
+//                                              kDiagonalBlockSize,
+//                                              kDiagonalBlockSize).norm();
+//         }
+//         if (diff > kTolerance) {
+//           return AssertionFailure()
+//               << "Preconditioner block " << i << " " << j << " differs "
+//               << "from expected value by " << diff;
+//         }
+//       }
+//     }
+//     return AssertionSuccess();
+//   }
+
+//   // Accessors
+//   int get_num_blocks() { return preconditioner_->num_blocks_; }
+
+//   int get_num_clusters() { return preconditioner_->num_clusters_; }
+//   int* get_mutable_num_clusters() { return &preconditioner_->num_clusters_; }
+
+//   const vector<int>& get_block_size() {
+//     return preconditioner_->block_size_; }
+
+//   vector<int>* get_mutable_block_size() {
+//     return &preconditioner_->block_size_; }
+
+//   const vector<int>& get_cluster_membership() {
+//     return preconditioner_->cluster_membership_;
+//   }
+
+//   vector<int>* get_mutable_cluster_membership() {
+//     return &preconditioner_->cluster_membership_;
+//   }
+
+//   const set<pair<int, int>>& get_block_pairs() {
+//     return preconditioner_->block_pairs_;
+//   }
+
+//   set<pair<int, int>>* get_mutable_block_pairs() {
+//     return &preconditioner_->block_pairs_;
+//   }
+
+//   const std::unordered_set<pair<int, int>, pair_hash>& get_cluster_pairs() {
+//     return preconditioner_->cluster_pairs_;
+//   }
+
+//   std::unordered_set<pair<int, int>, pair_hash>* get_mutable_cluster_pairs()
+//   {
+//     return &preconditioner_->cluster_pairs_;
+//   }
+
+//   bool IsBlockPairInPreconditioner(const int block1, const int block2) {
+//     return preconditioner_->IsBlockPairInPreconditioner(block1, block2);
+//   }
+
+//   bool IsBlockPairOffDiagonal(const int block1, const int block2) {
+//     return preconditioner_->IsBlockPairOffDiagonal(block1, block2);
+//   }
+
+//   const BlockRandomAccessSparseMatrix* get_m() {
+//     return preconditioner_->m_.get();
+//   }
+
+//   int num_rows_;
+//   int num_cols_;
+//   int num_eliminate_blocks_;
+//   int num_camera_blocks_;
+
+//   std::unique_ptr<BlockSparseMatrix> A_;
+//   std::unique_ptr<double[]> b_;
+//   std::unique_ptr<double[]> D_;
+
+//   Preconditioner::Options options_;
+//   std::unique_ptr<VisibilityBasedPreconditioner> preconditioner_;
+//   std::unique_ptr<BlockRandomAccessDenseMatrix> schur_complement_;
+// };
+
+// TEST_F(VisibilityBasedPreconditionerTest, OneClusterClusterJacobi) {
+//   options_.type = CLUSTER_JACOBI;
+//   preconditioner_.reset(
+//       new VisibilityBasedPreconditioner(*A_->block_structure(), options_));
+
+//   // Override the clustering to be a single clustering containing all
+//   // the cameras.
+//   vector<int>& cluster_membership = *get_mutable_cluster_membership();
+//   for (int i = 0; i < num_camera_blocks_; ++i) {
+//     cluster_membership[i] = 0;
+//   }
+
+//   *get_mutable_num_clusters() = 1;
+
+//   std::unordered_set<pair<int, int>, pair_hash>& cluster_pairs =
+//   *get_mutable_cluster_pairs(); cluster_pairs.clear();
+//   cluster_pairs.insert(make_pair(0, 0));
+
+//   EXPECT_TRUE(IsSparsityStructureValid());
+//   EXPECT_TRUE(PreconditionerValuesMatch());
+
+//   // Multiplication by the inverse of the preconditioner.
+//   const int num_rows = schur_complement_->num_rows();
+//   ConstMatrixRef full_schur_complement(schur_complement_->values(),
+//                                        num_rows,
+//                                        num_rows);
+//   Vector x(num_rows);
+//   Vector y(num_rows);
+//   Vector z(num_rows);
+
+//   for (int i = 0; i < num_rows; ++i) {
+//     x.setZero();
+//     y.setZero();
+//     z.setZero();
+//     x[i] = 1.0;
+//     preconditioner_->RightMultiply(x.data(), y.data());
+//     z = full_schur_complement
+//         .selfadjointView<Eigen::Upper>()
+//         .llt().solve(x);
+//     double max_relative_difference =
+//         ((y - z).array() / z.array()).matrix().lpNorm<Eigen::Infinity>();
+//     EXPECT_NEAR(max_relative_difference, 0.0, kTolerance);
+//   }
+// }
+
+// TEST_F(VisibilityBasedPreconditionerTest, ClusterJacobi) {
+//   options_.type = CLUSTER_JACOBI;
+//   preconditioner_.reset(
+//       new VisibilityBasedPreconditioner(*A_->block_structure(), options_));
+
+//   // Override the clustering to be equal number of cameras.
+//   vector<int>& cluster_membership = *get_mutable_cluster_membership();
+//   cluster_membership.resize(num_camera_blocks_);
+//   static const int kNumClusters = 3;
+
+//   for (int i = 0; i < num_camera_blocks_; ++i) {
+//     cluster_membership[i] = (i * kNumClusters) / num_camera_blocks_;
+//   }
+//   *get_mutable_num_clusters() = kNumClusters;
+
+//   std::unordered_set<pair<int, int>, pair_hash>& cluster_pairs =
+//   *get_mutable_cluster_pairs(); cluster_pairs.clear(); for (int i = 0; i <
+//   kNumClusters; ++i) {
+//     cluster_pairs.insert(make_pair(i, i));
+//   }
+
+//   EXPECT_TRUE(IsSparsityStructureValid());
+//   EXPECT_TRUE(PreconditionerValuesMatch());
+// }
+
+// TEST_F(VisibilityBasedPreconditionerTest, ClusterTridiagonal) {
+//   options_.type = CLUSTER_TRIDIAGONAL;
+//   preconditioner_.reset(
+//       new VisibilityBasedPreconditioner(*A_->block_structure(), options_));
+//   static const int kNumClusters = 3;
+
+//   // Override the clustering to be 3 clusters.
+//   vector<int>& cluster_membership = *get_mutable_cluster_membership();
+//   cluster_membership.resize(num_camera_blocks_);
+//   for (int i = 0; i < num_camera_blocks_; ++i) {
+//     cluster_membership[i] = (i * kNumClusters) / num_camera_blocks_;
+//   }
+//   *get_mutable_num_clusters() = kNumClusters;
+
+//   // Spanning forest has structure 0-1 2
+//   std::unordered_set<pair<int, int>, pair_hash>& cluster_pairs =
+//   *get_mutable_cluster_pairs(); cluster_pairs.clear(); for (int i = 0; i <
+//   kNumClusters; ++i) {
+//     cluster_pairs.insert(make_pair(i, i));
+//   }
+//   cluster_pairs.insert(make_pair(0, 1));
+
+//   EXPECT_TRUE(IsSparsityStructureValid());
+//   EXPECT_TRUE(PreconditionerValuesMatch());
+// }
+
+}  // namespace internal
+}  // namespace ceres