C++ Eigen库计算矩阵特征值及特征向量

#include <iostream>
#include <Eigen/Dense>
#include <Eigen/Eigenvalues>
using namespace Eigen;
using namespace std;

void Eig()
{
 Matrix3d A;
 A << 1, 2, 3, 4, 5, 6, 7, 8, 9;
 cout << "Here is a 3x3 matrix, A:" << endl << A << endl << endl;
 EigenSolver<Matrix3d> es(A);
 
 Matrix3d D = es.pseudoEigenvalueMatrix();
 Matrix3d V = es.pseudoEigenvectors();
 cout << "The pseudo-eigenvalue matrix D is:" << endl << D << endl;
 cout << "The pseudo-eigenvector matrix V is:" << endl << V << endl;
 cout << "Finally, V * D * V^(-1) = " << endl << V * D * V.inverse() << endl;
}
int main()
{

 Eig();
 
}

//maxCoeff
//minCoeff

int col_index, row_index;
cout << D.maxCoeff(&row_index, &col_index) << endl;
cout << row_index << " " << col_index << endl;

clear all
clc
A = [1 2 3;4 5 6;7 8 9]
[V,D] = eig(A)

A = magic(6);
[V,D] = eig(A)
[D_S,index] = sort(diag(D),'descend')
V_S = V(:,index)

V =

 0.4082 -0.2887 0.4082 0.1507 0.4714 -0.4769
 0.4082 0.5774 0.4082 0.4110 0.4714 -0.4937
 0.4082 -0.2887 0.4082 -0.2602 -0.2357 0.0864
 0.4082 0.2887 -0.4082 0.4279 -0.4714 0.1435
 0.4082 -0.5774 -0.4082 -0.7465 -0.4714 0.0338
 0.4082 0.2887 -0.4082 0.0171 0.2357 0.7068


D =

 111.0000   0   0   0   0   0
   0 27.0000   0   0   0   0
   0   0 -27.0000   0   0   0
   0   0   0 9.7980   0   0
   0   0   0   0 -0.0000   0
   0   0   0   0   0 -9.7980


D_S =

 111.0000
 27.0000
 9.7980
 -0.0000
 -9.7980
 -27.0000


V_S =

 0.4082 -0.2887 0.1507 0.4714 -0.4769 0.4082
 0.4082 0.5774 0.4110 0.4714 -0.4937 0.4082
 0.4082 -0.2887 -0.2602 -0.2357 0.0864 0.4082
 0.4082 0.2887 0.4279 -0.4714 0.1435 -0.4082
 0.4082 -0.5774 -0.7465 -0.4714 0.0338 -0.4082
 0.4082 0.2887 0.0171 0.2357 0.7068 -0.4082