bring over phonelibs minus frida-gum and qsml

phonelibs/eigen/unsupported/doc/examples/MatrixSquareRoot.cpp

@@ -0,0 +1,16 @@
+#include <unsupported/Eigen/MatrixFunctions>
+#include <iostream>
+
+using namespace Eigen;
+
+int main()
+{
+  const double pi = std::acos(-1.0);
+
+  MatrixXd A(2,2);
+  A << cos(pi/3), -sin(pi/3), 
+       sin(pi/3),  cos(pi/3);
+  std::cout << "The matrix A is:\n" << A << "\n\n";
+  std::cout << "The matrix square root of A is:\n" << A.sqrt() << "\n\n";
+  std::cout << "The square of the last matrix is:\n" << A.sqrt() * A.sqrt() << "\n";
+}