Squashed 'third_party/eigen/' changes from 61d72f6..cf794d3


Change-Id: I9b814151b01f49af6337a8605d0c42a3a1ed4c72
git-subtree-dir: third_party/eigen
git-subtree-split: cf794d3b741a6278df169e58461f8529f43bce5d
diff --git a/doc/snippets/SparseMatrix_coeffs.cpp b/doc/snippets/SparseMatrix_coeffs.cpp
new file mode 100644
index 0000000..f71a69b
--- /dev/null
+++ b/doc/snippets/SparseMatrix_coeffs.cpp
@@ -0,0 +1,9 @@
+SparseMatrix<double> A(3,3);
+A.insert(1,2) = 0;
+A.insert(0,1) = 1;
+A.insert(2,0) = 2;
+A.makeCompressed();
+cout << "The matrix A is:" << endl << MatrixXd(A) << endl;
+cout << "it has " << A.nonZeros() << " stored non zero coefficients that are: " << A.coeffs().transpose() << endl;
+A.coeffs() += 10;
+cout << "After adding 10 to every stored non zero coefficient, the matrix A is:" << endl << MatrixXd(A) << endl;