C++矩阵处理工具——Eigen .

Eigen是C++中可以用来调用并进行矩阵计算的一个库，里面封装了一些类，需要的头文件和功能如下：



 

Eigen的配置



 

Eigen的应用举例：
Eigen下载地址

Eigen的应用举例：整理的一些常用操作，基本的矩阵运算就在下面了，算是个入门吧~主要分以下几部分：



建议大家放到编译环境里去看，因为我这里有一些region的东西，编译器下更方便看~

#include <iostream>
#include <Eigen/Dense>

//using Eigen::MatrixXd;
using namespace Eigen;
using namespace Eigen::internal;
using namespace Eigen::Architecture;

using namespace std;

int main()
{

#pragma region one_d_object

cout<<"*******************1D-object****************"<<endl;

Vector4d v1;
v1<< 1,2,3,4;
cout<<"v1=\n"<<v1<<endl;

VectorXd v2(3);
v2<<1,2,3;
cout<<"v2=\n"<<v2<<endl;

Array4i v3;
v3<<1,2,3,4;
cout<<"v3=\n"<<v3<<endl;

ArrayXf v4(3);
v4<<1,2,3;
cout<<"v4=\n"<<v4<<endl;

#pragma endregion

#pragma region two_d_object

cout<<"*******************2D-object****************"<<endl;
//2D objects:
MatrixXd m(2,2);

//method 1
m(0,0) = 3;
m(1,0) = 2.5;
m(0,1) = -1;
m(1,1) = m(1,0) + m(0,1);

//method 2
m<<3,-1,
2.5,-1.5;
cout <<"m=\n"<< m << endl;

#pragma endregion

#pragma region Comma_initializer

cout<<"*******************Initialization****************"<<endl;

int rows=5;
int cols=5;
MatrixXf m1(rows,cols);
m1<<( Matrix3f()<<1,2,3,4,5,6,7,8,9 ).finished(),
MatrixXf::Zero(3,cols-3),
MatrixXf::Zero(rows-3,3),
MatrixXf::Identity(rows-3,cols-3);
cout<<"m1=\n"<<m1<<endl;

#pragma endregion

#pragma region Runtime_info

cout<<"*******************Runtime Info****************"<<endl;

MatrixXf m2(5,4);
m2<<MatrixXf::Identity(5,4);
cout<<"m2=\n"<<m2<<endl;

MatrixXf m3;
m3=m1*m2;
cout<<"m3.rows()="<<m3.rows()<<"  ;  "
<<"m3.cols()="<< m3.cols()<<endl;

cout<<"m3=\n"<<m3<<endl;

#pragma endregion

#pragma region Resizing

cout<<"*******************Resizing****************"<<endl;

//1D-resize
v1.resize(4);
cout<<"Recover v1 to 4*1 array : v1=\n"<<v1<<endl;

//2D-resize
m.resize(2,3);
m.resize(Eigen::NoChange, 3);
m.resizeLike(m2);
m.resize(2,2);

#pragma endregion

#pragma region Coeff_access

cout<<"*******************Coefficient access****************"<<endl;

float tx=v1(1);
tx=m1(1,1);
cout<<endl;

#pragma endregion

#pragma  region Predefined_matrix

cout<<"*******************Predefined Matrix****************"<<endl;

//1D-object
typedef  Matrix3f   FixedXD;
FixedXD x;

x=FixedXD::Zero();
x=FixedXD::Ones();
x=FixedXD::Constant(tx);//tx is the value
x=FixedXD::Random();
cout<<"x=\n"<<x<<endl;

typedef ArrayXf Dynamic1D;
//或者 typedef VectorXf Dynamic1D
int size=3;
Dynamic1D xx;
xx=Dynamic1D::Zero(size);
xx=Dynamic1D::Ones(size);
xx=Dynamic1D::Constant(size,tx);
xx=Dynamic1D::Random(size);
cout<<"xx=\n"<<x<<endl;

//2D-object
typedef MatrixXf Dynamic2D;
Dynamic2D y;
y=Dynamic2D::Zero(rows,cols);
y=Dynamic2D::Ones(rows,cols);
y=Dynamic2D::Constant(rows,cols,tx);//tx is the value
y=Dynamic2D::Random(rows,cols);

#pragma endregion

#pragma region Arithmetic_Operators

cout<<"******************* Arithmetic_Operators****************"<<endl;

//add & sub
MatrixXf m4(5,4);
MatrixXf m5;
m4=m2+m3;
m3-=m2;

//product
m3=m1*m2;

//transposition
m5=m4.transpose();
//m5=m.adjoint();//伴随矩阵

//dot product
double xtt;
cout<<"v1=\n"<<v1<<endl;
v2.resize(4);
v2<<VectorXd::Ones(4);
cout<<"v2=\n"<<v2<<endl;

cout<<"*************dot product*************"<<endl;
xtt=v1.dot(v2);
cout<<"v1.*v2="<<xtt<<endl;

//vector norm

cout<<"*************matrix norm*************"<<endl;
xtt=v1.norm();
cout<<"norm of v1="<<xtt<<endl;
xtt=v1.squaredNorm();
cout<<"SquareNorm of v1="<<xtt<<endl;

#pragma endregion

cout<<endl;
}