From 52dce0c126e67583a349e87a3f5eedee9de92dc7 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Wed, 20 Jun 2012 09:28:32 +0200
Subject: significantly extend the tutorial of sparse matrices

---
 doc/special_examples/Tutorial_sparse_example.cpp | 32 ++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 doc/special_examples/Tutorial_sparse_example.cpp

(limited to 'doc/special_examples/Tutorial_sparse_example.cpp')

diff --git a/doc/special_examples/Tutorial_sparse_example.cpp b/doc/special_examples/Tutorial_sparse_example.cpp
new file mode 100644
index 000000000..002f19f01
--- /dev/null
+++ b/doc/special_examples/Tutorial_sparse_example.cpp
@@ -0,0 +1,32 @@
+#include <Eigen/Sparse>
+#include <vector>
+
+typedef Eigen::SparseMatrix<double> SpMat; // declares a column-major sparse matrix type of double
+typedef Eigen::Triplet<double> T;
+
+void buildProblem(std::vector<T>& coefficients, Eigen::VectorXd& b, int n);
+void saveAsBitmap(const Eigen::VectorXd& x, int n, const char* filename);
+
+int main(int argc, char** argv)
+{
+  int n = 300;  // size of the image
+  int m = n*n;  // number of unknows (=number of pixels)
+
+  // Assembly:
+  std::vector<T> coefficients;            // list of non-zeros coefficients
+  Eigen::VectorXd b(m);                   // the right hand side-vector resulting from the constraints
+  buildProblem(coefficients, b, n);
+
+  SpMat A(m,m);
+  A.setFromTriplets(coefficients.begin(), coefficients.end());
+
+  // Solving:
+  Eigen::SimplicialCholesky<SpMat> chol(A);  // performs a Cholesky factorization of A
+  Eigen::VectorXd x = chol.solve(b);         // use the factorization to solve for the given right hand side
+
+  // Export the result to a file:
+  saveAsBitmap(x, n, argv[1]);
+
+  return 0;
+}
+
-- 
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