最近和一些朋友討論到了C++中數學工具的問題,以前總是很2地自己寫矩陣運算,或者有時候在matlab裏計算了一些數據再往C程序裏倒,唉~想想那些年,我們白寫的代碼啊……人家早已封裝好了!首先推薦幾個可以在C++中調用的數學平臺:eigen、bias、lapack、svd、CMatrix,本文着重eigen做以講解,希望對各位有所幫助。
下面是本文主線,主要圍繞下面幾點進行講解:
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Eigen是什麼?
Eigen3哪裏下載?
Eigen3的配置
Eigen3 樣例代碼有沒有?
去哪裏更深入學習?
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Eigen是什麼?
Eigen是C++中可以用來調用並進行矩陣計算的一個庫,裏面封裝了一些類,需要的頭文件和功能如下:
Eigen的主頁上有一些更詳細的Eigen介紹。
Eigen3哪裏下載?
這裏是我下好的,這裏是官網主頁,請自行下載,是個code包,不用安裝。
Eigen的配置
直接上圖了,附加包含目錄那裏填上你放Eigen文件夾的位置即可。
Eigen的樣例代碼有沒有?
當然有,這篇文章重點就是這裏!
以下是我整理的一些常用操作,基本的矩陣運算就在下面了,算是個入門吧~主要分以下幾部分:
建議大家放到編譯環境裏去看,因爲我這裏有一些region的東西,編譯器下更方便看~
- #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();//伴隨矩陣
- //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;
- }
Please refer to Eigen中的類及函數