// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2010, 2011, 2012 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
//
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// modification, are permitted provided that the following conditions are met:
//
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//   this list of conditions and the following disclaimer.
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//   and/or other materials provided with the distribution.
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//   used to endorse or promote products derived from this software without
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// Author: sameeragarwal@google.com (Sameer Agarwal)

#include "ceres/schur_ordering.h"

#include "ceres/graph.h"
#include "ceres/graph_algorithms.h"
#include "ceres/internal/scoped_ptr.h"
#include "ceres/map_util.h"
#include "ceres/parameter_block.h"
#include "ceres/program.h"
#include "ceres/residual_block.h"
#include "glog/logging.h"

namespace ceres {
namespace internal {

int ComputeSchurOrdering(const Program& program,
                         vector<ParameterBlock*>* ordering) {
  CHECK_NOTNULL(ordering)->clear();

  scoped_ptr<Graph< ParameterBlock*> > graph(
      CHECK_NOTNULL(CreateHessianGraph(program)));
  int independent_set_size = IndependentSetOrdering(*graph, ordering);
  const vector<ParameterBlock*>& parameter_blocks = program.parameter_blocks();

  // Add the excluded blocks to back of the ordering vector.
  for (int i = 0; i < parameter_blocks.size(); ++i) {
    ParameterBlock* parameter_block = parameter_blocks[i];
    if (parameter_block->IsConstant()) {
      ordering->push_back(parameter_block);
    }
  }

  return independent_set_size;
}

Graph<ParameterBlock*>*
CreateHessianGraph(const Program& program) {
  Graph<ParameterBlock*>* graph = new Graph<ParameterBlock*>;
  const vector<ParameterBlock*>& parameter_blocks = program.parameter_blocks();
  for (int i = 0; i < parameter_blocks.size(); ++i) {
    ParameterBlock* parameter_block = parameter_blocks[i];
    if (!parameter_block->IsConstant()) {
      graph->AddVertex(parameter_block);
    }
  }

  const vector<ResidualBlock*>& residual_blocks = program.residual_blocks();
  for (int i = 0; i < residual_blocks.size(); ++i) {
    const ResidualBlock* residual_block = residual_blocks[i];
    const int num_parameter_blocks = residual_block->NumParameterBlocks();
    ParameterBlock* const* parameter_blocks =
        residual_block->parameter_blocks();
    for (int j = 0; j < num_parameter_blocks; ++j) {
      if (parameter_blocks[j]->IsConstant()) {
        continue;
      }

      for (int k = j + 1; k < num_parameter_blocks; ++k) {
        if (parameter_blocks[k]->IsConstant()) {
          continue;
        }

        graph->AddEdge(parameter_blocks[j], parameter_blocks[k]);
      }
    }
  }

  return graph;
}

}  // namespace internal
}  // namespace ceres