1 #include <Eigen/Sparse> 2 #include <vector> 3 #include <QImage> 4 5 typedef Eigen::SparseMatrix<double> SpMat; // declares a column-major sparse matrix type of double 6 typedef Eigen::Triplet<double> T; 7 8 void insertCoefficient(int id, int i, int j, double w, std::vector<T>& coeffs, 9 Eigen::VectorXd& b, const Eigen::VectorXd& boundary) 10 { 11 int n = boundary.size(); 12 int id1 = i+j*n; 13 14 if(i==-1 || i==n) b(id) -= w * boundary(j); // constrained coefficient 15 else if(j==-1 || j==n) b(id) -= w * boundary(i); // constrained coefficient 16 else coeffs.push_back(T(id,id1,w)); // unknown coefficient 17 } 18 19 void buildProblem(std::vector<T>& coefficients, Eigen::VectorXd& b, int n) 20 { 21 b.setZero(); 22 Eigen::ArrayXd boundary = Eigen::ArrayXd::LinSpaced(n, 0,M_PI).sin().pow(2); 23 for(int j=0; j<n; ++j) 24 { 25 for(int i=0; i<n; ++i) 26 { 27 int id = i+j*n; 28 insertCoefficient(id, i-1,j, -1, coefficients, b, boundary); 29 insertCoefficient(id, i+1,j, -1, coefficients, b, boundary); 30 insertCoefficient(id, i,j-1, -1, coefficients, b, boundary); 31 insertCoefficient(id, i,j+1, -1, coefficients, b, boundary); 32 insertCoefficient(id, i,j, 4, coefficients, b, boundary); 33 } 34 } 35 } 36 37 void saveAsBitmap(const Eigen::VectorXd& x, int n, const char* filename) 38 { 39 Eigen::Array<unsigned char,Eigen::Dynamic,Eigen::Dynamic> bits = (x*255).cast<unsigned char>(); 40 QImage img(bits.data(), n,n,QImage::Format_Indexed8); 41 img.setColorCount(256); 42 for(int i=0;i<256;i++) img.setColor(i,qRgb(i,i,i)); 43 img.save(filename); 44 } 45
