Tutorial_sparse_example_details.cpp File Reference

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Typedefs
typedef Eigen::SparseMatrix< double >	SpMat
typedef Eigen::Triplet< double >	T

Functions
void	buildProblem (std::vector< T > &coefficients, Eigen::VectorXd &b, int n)
void	insertCoefficient (int id, int i, int j, double w, std::vector< T > &coeffs, Eigen::VectorXd &b, const Eigen::VectorXd &boundary)
void	saveAsBitmap (const Eigen::VectorXd &x, int n, const char *filename)

Typedef Documentation

SpMat

typedef Eigen::SparseMatrix<double> SpMat

Definition at line 5 of file Tutorial_sparse_example_details.cpp.

T

typedef Eigen::Triplet<double> T

Definition at line 6 of file Tutorial_sparse_example_details.cpp.

Function Documentation

buildProblem()

void buildProblem	(	std::vector< T > &	coefficients,
		Eigen::VectorXd &	b,
		int	n
	)

Definition at line 19 of file Tutorial_sparse_example_details.cpp.

{
  b.setZero();
  Eigen::ArrayXd boundary = Eigen::ArrayXd::LinSpaced(n, 0,M_PI).sin().pow(2);
  for(int j=0; j<n; ++j)
  {
    for(int i=0; i<n; ++i)
    {
      int id = i+j*n;
      insertCoefficient(id, i-1,j, -1, coefficients, b, boundary);
      insertCoefficient(id, i+1,j, -1, coefficients, b, boundary);
      insertCoefficient(id, i,j-1, -1, coefficients, b, boundary);
      insertCoefficient(id, i,j+1, -1, coefficients, b, boundary);
      insertCoefficient(id, i,j,    4, coefficients, b, boundary);
    }
  }
}

insertCoefficient()

void insertCoefficient	(	int	id,
		int	i,
		int	j,
		double	w,
		std::vector< T > &	coeffs,
		Eigen::VectorXd &	b,
		const Eigen::VectorXd &	boundary
	)

Definition at line 8 of file Tutorial_sparse_example_details.cpp.

{
  int n = int(boundary.size());
  int id1 = i+j*n;
 
        if(i==-1 || i==n) b(id) -= w * boundary(j); // constrained coefficient
  else  if(j==-1 || j==n) b(id) -= w * boundary(i); // constrained coefficient
  else  coeffs.push_back(T(id,id1,w));              // unknown coefficient
}

saveAsBitmap()

void saveAsBitmap	(	const Eigen::VectorXd &	x,
		int	n,
		const char *	filename
	)

Definition at line 37 of file Tutorial_sparse_example_details.cpp.

{
  Eigen::Array<unsigned char,Eigen::Dynamic,Eigen::Dynamic> bits = (x*255).cast<unsigned char>();
  QImage img(bits.data(), n,n,QImage::Format_Indexed8);
  img.setColorCount(256);
  for(int i=0;i<256;i++) img.setColor(i,qRgb(i,i,i));
  img.save(filename);
}