# 数学软件quiz

**Repository Path**: uranium235/mathematical-software-quiz

## Basic Information

- **Project Name**: 数学软件quiz
- **Description**: 数学软件课程期末quiz代码
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 1
- **Created**: 2023-02-09
- **Last Updated**: 2023-02-09

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

项目地址：https://gitee.com/liu-zhifang2333/mathematical-software-quiz.git

## section1

```c++
#include <iostream>
#include <cmath>
#include <stdio.h>
#include <lapack.h>
#include <lapacke_config.h>
#include <lapacke_utils.h>
using namespace std;

extern lapack_int LAPACKE_dgeev( int matrix_order, char jobvl, char jobvr, lapack_int n, double* a, lapack_int lda, double* wr, double* wi, double* vl, lapack_int ldvl, double* vr, lapack_int ldvr);

int main()
{
    int matrix_order = LAPACK_COL_MAJOR;
    char jobvl = 'N';
    char jobvr = 'V';
    int n = 50;
    double A[2500];
    for(int i = 0;i<50;i++)
    {
        for(int j = 0;i<50;i++)
        {
            A[i*50+j] = 0;
        }
    }
    A[0] = 3;
    A[1] = 1;
    for(int i = 1;i<49;i++)
    {
        A[i*51] = 3;
        A[i*51+1] = 1;
        A[i*51-1] = 1;
    }
    A[49*51] = 3;
    A[49*51-1] = 1;
    int lda = n;
    double wr[50];
    double wi[50];
    for(int i = 0;i<50;i++)
    {
        wr[i] = 0;
        wi[i] = 0;
    }
    double vl[2500];
    int ldvl = 50;
    double vr[2500];
    int ldvr = 50;

    int info = LAPACKE_dgeev(matrix_order,jobvl,jobvr,n,A,lda,wr,wi,vl,ldvl,vr,ldvr);
    if(info==0)
    {
        int i = 0;
        int j = 0;
        for(i=0;i<n;i++)
        {
            cout << "eigenvalue" << i << ":" << endl;
            cout << wr[i] << " + i " << wi[i] << endl;
        }
    }
    cout << "complete" << endl;
    
    return 0;
}
```

编译及运行命令：

```
g++ -o ex1.o -c ex1.cpp
g++ -o ex1 ex1.o -llapack -lgfortran
./ex1
```



## section2

```c++
#include <iostream>
#include <ostream>
#include <eigen3/Eigen/Dense>
#include <eigen3/Eigen/Core>
using namespace std;
using namespace Eigen;

int main(int argc, char const *argv[]
{
    MatrixXd A;
    MatrixXd b;
    MatrixXd x;
    x = A.colPivHouseholderQr().solve(b)
    ofstream outfile("data0.csv");
    if(!outfile)
    {
        cout << "打开文件夹失败！" << endl;
        exit(1);
    }
    for(int q = 0;q<n;q++)
    {
        outfile << x[q] << endl;
    }
    outfile.close();
}
```

使用了Eigen的函数，用QR分解的方法解了稀疏矩阵Ax=b。

其中，A和b用octave提取

```
>>[i,j,s] = A
>>dimwrite('A.csv',[i,j,s])
>>dimwritee('b.csv',b,'precision',''%f')
```