diff options
author | Gael Guennebaud <g.gael@free.fr> | 2012-06-20 09:28:32 +0200 |
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committer | Gael Guennebaud <g.gael@free.fr> | 2012-06-20 09:28:32 +0200 |
commit | 52dce0c126e67583a349e87a3f5eedee9de92dc7 (patch) | |
tree | 6f27c66cecfec258f22d096835424d6fa324f9fa /doc/special_examples/Tutorial_sparse_example_details.cpp | |
parent | 882912b85f7ea310fd76689d7e55b8f88e6d3cab (diff) |
significantly extend the tutorial of sparse matrices
Diffstat (limited to 'doc/special_examples/Tutorial_sparse_example_details.cpp')
-rw-r--r-- | doc/special_examples/Tutorial_sparse_example_details.cpp | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/doc/special_examples/Tutorial_sparse_example_details.cpp b/doc/special_examples/Tutorial_sparse_example_details.cpp new file mode 100644 index 000000000..8c3020b63 --- /dev/null +++ b/doc/special_examples/Tutorial_sparse_example_details.cpp @@ -0,0 +1,44 @@ +#include <Eigen/Sparse> +#include <vector> +#include <QImage> + +typedef Eigen::SparseMatrix<double> SpMat; // declares a column-major sparse matrix type of double +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 = boundary.size(); + int id1 = i+j*n; + + if(i==-1 || i==n) b(id) -= w * boundary(j); // constrained coeffcieint + else if(j==-1 || j==n) b(id) -= w * boundary(i); // constrained coeffcieint + 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 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); +} |