| Quellcodebibliothek Statistik Leitseite products/Sources/formale Sprachen/C/MySQL/doc/special_examples/ (MySQL Server Version 8.1-8.4©) Datei vom 12.11.2025 mit Größe 1 kB |
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Quelle Tutorial_sparse_example_details.cpp Sprache: C |
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#include <Eigen/Sparse>
#include <vector> #include <QImage> typedef Eigen::SparseMatrix<double> SpMat; // declares a column-major sparse matrix type of d typedef Eigen::Triplet<double> T; void insertCoefficient(int id, int i, int j, double w, std::vector<T>& coeffs, Eigen::VectorXd& b, const Eigen::VectorXd& boundary) { 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 } void buildProblem(std::vector<T>& coefficients, Eigen::VectorXd& b, int n) { 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); } } } void saveAsBitmap(const Eigen::VectorXd& x, int n, const char* filename) { Eigen::Array<unsigned char,Eigen::Dynamic,Eigen::Dynamic> bits = (x*255).cast<unsigned c 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); } ¤ Dauer der Verarbeitung: 0.2 Sekunden (vorverarbeitet) ¤*© Formatika GbR, Deutschland |
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2026-03-28