Complete LU documentation
diff --git a/doc/snippets/LU_kernel.cpp b/doc/snippets/LU_kernel.cpp
new file mode 100644
index 0000000..e01186d
--- /dev/null
+++ b/doc/snippets/LU_kernel.cpp
@@ -0,0 +1,7 @@
+MatrixXf m = MatrixXf::Random(3,5);
+cout << "Here is the matrix m:" << endl << m << endl;
+MatrixXf ker = m.lu().kernel();
+cout << "Here is a matrix whose columns form a basis of the kernel of m:"
+ << endl << ker << endl;
+cout << "By definition of the kernel, m*ker is zero:"
+ << endl << m*ker << endl;