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

// Copyright 2015 Google Inc. All rights reserved.

// http://ceres-solver.org/

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// Author: kushalav@google.com (Avanish Kushal)

//         sameeragarwal@google.com (Sameer Agarwal)

//

// Functions to manipulate visibility information from the block

// structure of sparse matrices.

#ifndef CERES_INTERNAL_VISIBILITY_H_

#define CERES_INTERNAL_VISIBILITY_H_

#include <set>

#include <vector>

#include "ceres/graph.h"

namespace ceres {

namespace internal {

struct CompressedRowBlockStructure;

// Given a compressed row block structure, computes the set of

// e_blocks "visible" to each f_block. If an e_block co-occurs with an

// f_block in a residual block, it is visible to the f_block. The

// first num_eliminate_blocks columns blocks are e_blocks and the rest

// f_blocks.

//

// In a structure from motion problem, e_blocks correspond to 3D

// points and f_blocks correspond to cameras.

void ComputeVisibility(const CompressedRowBlockStructure& block_structure,

                       int num_eliminate_blocks,

                       std::vector<std::set<int> >* visibility);

// Given f_block visibility as computed by the ComputeVisibility

// function above, construct and return a graph whose vertices are

// f_blocks and an edge connects two vertices if they have atleast one

// e_block in common. The weight of this edge is normalized dot

// product between the visibility vectors of the two

// vertices/f_blocks.

//

// This graph reflects the sparsity structure of reduced camera

// matrix/Schur complement matrix obtained by eliminating the e_blocks

// from the normal equations.

//

// Caller acquires ownership of the returned WeightedGraph pointer

// (heap-allocated).

WeightedGraph<int>* CreateSchurComplementGraph(

    const std::vector<std::set<int> >& visibility);

}  // namespace internal

}  // namespace ceres

#endif  // CERES_INTERNAL_VISIBILITY_H_