规范模块目录和第三方依赖结构

third_party/eigen3/doc/examples/TutorialLinAlgRankRevealing.cpp

@@ -0,0 +1,20 @@
+#include <iostream>
+#include <Eigen/Dense>
+
+using namespace std;
+using namespace Eigen;
+
+int main()
+{
+   Matrix3f A;
+   A << 1, 2, 5,
+        2, 1, 4,
+        3, 0, 3;
+   cout << "Here is the matrix A:\n" << A << endl;
+   FullPivLU<Matrix3f> lu_decomp(A);
+   cout << "The rank of A is " << lu_decomp.rank() << endl;
+   cout << "Here is a matrix whose columns form a basis of the null-space of A:\n"
+        << lu_decomp.kernel() << endl;
+   cout << "Here is a matrix whose columns form a basis of the column-space of A:\n"
+        << lu_decomp.image(A) << endl; // yes, have to pass the original A
+}