Eigen库学习笔记（三）

• 1、从官网示例开始
• • A simple first program
  • Example 2: Matrices and vectors

Eigen是有关线性代数（矩阵、向量等）的c++模板库。支持SSE2/3/4, ARM NEON (32-bit and 64-bit), PowerPC AltiVec/VSX (32-bit and 64-bit) instruction sets, S390x SIMD (ZVector)

1、从官网示例开始

A simple first program

2*2矩阵定义与赋值

#include <iostream>
#include <Eigen/Dense>
 
using Eigen::MatrixXd;
 
int main()
{
  MatrixXd m(2,2);
  m(0,0) = 3;
  m(1,0) = 2.5;
  m(0,1) = -1;
  m(1,1) = m(1,0) + m(0,1);
  std::cout << m << std::endl;
}

Example 2: Matrices and vectors

Size set at run time:

#include <iostream>
#include <Eigen/Dense>
 
using namespace Eigen;
using namespace std;
 
int main()
{
  MatrixXd m = MatrixXd::Random(3,3);
  m = (m + MatrixXd::Constant(3,3,1.2)) * 50;
  cout << "m =" << endl << m << endl;
  VectorXd v(3);
  v << 1, 2, 3;
  cout << "m * v =" << endl << m * v << endl;
}

Size set at compile time:

#include <iostream>
#include <Eigen/Dense>
 
using namespace Eigen;
using namespace std;
 
int main()
{
  Matrix3d m = Matrix3d::Random();
  m = (m + Matrix3d::Constant(1.2)) * 50;
  cout << "m =" << endl << m << endl;
  Vector3d v(1,2,3);
  
  cout << "m * v =" << endl << m * v << endl;
}

运行输出：

m =
  94 89.8 43.5
49.4  101 86.8
88.3 29.8 37.8
m * v =
404
512
261

参考：Eigen 3.4.0