// Ceres Solver - A fast non-linear least squares minimizer
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// http://code.google.com/p/ceres-solver/
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// Author: sameeragarwal@google.com (Sameer Agarwal)
//
// Compute a parameter block ordering for use with the Schur
// complement based algorithms.

#ifndef CERES_INTERNAL_SCHUR_ORDERING_H_
#define CERES_INTERNAL_SCHUR_ORDERING_H_

#include <vector>
#include "ceres/graph.h"
#include "ceres/types.h"

namespace ceres {
namespace internal {

class Program;
class ParameterBlock;

// Uses an approximate independent set ordering to order the parameter
// blocks of a problem so that it is suitable for use with Schur
// complement based solvers. The output variable ordering contains an
// ordering of the parameter blocks and the return value is size of
// the independent set or the number of e_blocks (see
// schur_complement_solver.h for an explanation). Constant parameters
// are added to the end.
//
// The ordering vector has the structure
//
// ordering = [independent set,
//             complement of the independent set,
//             fixed blocks]
int ComputeSchurOrdering(const Program& program,
                         vector<ParameterBlock* >* ordering);


// Builds a graph on the parameter blocks of a Problem, whose
// structure reflects the sparsity structure of the Hessian. Each
// vertex corresponds to a parameter block in the Problem except for
// parameter blocks that are marked constant. An edge connects two
// parameter blocks, if they co-occur in a residual block.
Graph<ParameterBlock*>* CreateHessianGraph(const Program& program);

}  // namespace internal
}  // namespace ceres

#endif  // CERES_INTERNAL_SCHUR_ORDERING_H_