Question

我曾尝试编写从nxn矩阵中读取值的代码，然后将这些值打印出来。我想我已经成功地做到了这一点。我尝试的下一步是使用高斯消元法求解矩阵但我无法获得打印出值的代码。有人可以看看这个并告诉我哪里出错了吗？

  #include <cstdlib>
  #include <cmath>
  #include <vector>
  #include <iostream>
  #include <fstream>
  #include <string>

  using namespace std;


   int main(){
   //create a 2D vector of doubles 
   vector< vector< double > > matrix; 


    int num_lines = 0;
    double temporary, r;
    int i, j, k, dimension, temp; /* counter variables for loops */




    // Open a file containing the matrix data
    ifstream myFile("test_data2.txt");
    // Check if file is open
    if(myFile.is_open()){
    // First step is to detect matrix size by assuming matrix is
    // square and counting number of columns.

    // Tempoary variable to hold current line to process
    string line;

    // Tempoary variable to hold number of rows and cols in square matrix
    int num_lines = 0;

    // Count rows / cols
    while(getline(myFile, line)){
        num_lines ++;
    }

    // Reset EOF flag
    myFile.clear();

    // Reset to start of file
    myFile.seekg(0, myFile.beg);

    // Second step is to grab lines from the file and process them
    // splitting each line into substrings and converting them into
    // doubles

    // For each line
    for(int l = 0; l < num_lines; l ++){
        // Process line by line
        getline(myFile, line);

        // Tempoary vector to hold rows of matrix data
        vector<double> temp;

        // Tempoary variable to hold search positions
        int start = 0;
        int end;
        int length;

        // Get value by value
        for(int n = 0; n < num_lines; n ++){
            // Break line down by finding commas
            end = line.find(',', start);
            length = end - start;

            // Extract substring
            string tempstr = line.substr(start, length);

            // Set next value of start
            start = end + 1;

            // Convert to double
            temp.push_back(atof(tempstr.c_str()));
        }

        // Add row to matrix
        matrix.push_back(temp);
    }
    // Close input file
    myFile.close();
} else {
    // If input file failed to open, print an error
    cout << "Error opening input file" << endl;
}
// Print out the matrix (will do nothing if input file open failed)
cout << "Print out input file." << endl;

for(int i = 0; i < matrix.size(); i ++)
{
    for(int j = 0; j < matrix[i].size(); j ++)
    {
        cout << matrix[i][j];
        // Add commas and new lines when required
        // Remember not to add commas after rightmost values, or
        // a new line at the end of the last value
        if(j < matrix[i].size() - 1)
        {
            cout << ' '; // Character, not string
        }
        else
        {
            if(i < matrix[i].size() - 1)
            {
                cout << '\n'; // Character, not string
            }
        }
    }
}






 for (i = 0; i < num_lines; i++)
    for (j = num_lines; j < 2 * num_lines; j++)
        if (i == j % num_lines)
            matrix[i][j] = 1;
        else
            matrix[i][j] = 0;

  /* using gauss-jordan elimination */
  for (j = 0; j < num_lines; j++) {
    temp = j;

    /* finding maximum jth column element in last (dimension-j) rows */
    for (i = j + 1; i < num_lines; i++)
        if (matrix[i][j] > matrix[temp][j])
            temp = i;



    /* swapping row which has maximum jth column element */
    if (temp != j)
        for (k = 0; k < 2 * num_lines; k++) {
            temporary = matrix[j][k];
            matrix[j][k] = matrix[temp][k];
            matrix[temp][k] = temporary;
        }

      /* performing row operations to form required identity matrix out of the input              matrix */
    for (i = 0; i < num_lines; i++)
        if (i != j) {
            r = matrix[i][j];
            for (k = 0; k < 2 * num_lines; k++)
                matrix[i][k] -= matrix[j][k] * r / matrix[j][j];
        } else {
            r = matrix[i][j];
            for (k = 0; k < 2 * dimension; k++)
                matrix[i][k] /= r;
        }
   }

   /* Display augmented matrix */
   printf("\n After Gauss-Jordan elimination, augmented matrix is : \n\n");

  for (i = 0; i < num_lines; i++) {
     for (j = 0; j < 2 * num_lines; j++)
        printf("  %4.2f", matrix[i][j]);
      printf("\n");
   }


   /* displaying inverse of the non-singular matrix */
   printf("\n\n\n The inverse of the entered non-singular matrix is : \n\n");

    for (i = 0; i < num_lines; i++) {
    for (j = num_lines; j < 2 * num_lines; j++)
        printf("  %.5f", matrix[i][j]);
    printf("\n");
  }


 return 0;
  }

    // EXAMPLE FILE
    //1,2,3
    //4.5,6.7,8.8
    //-110,-55.3,+53.723
    // END OF EXAMPLE FILE REMOVE COMMENTS AT TOP AND BOTTOM AND "//" characters before    use. Save as "matrix.csv".

Answer 1

BUG1：

您声明了

 int num_lines = 0;

里面的

 if(myFile.is_open())

块。因此，'num_lines ++'行在

中递增此变量

 while(getline(....) )

循环，但然后num_lines（第二个）得到未声明，所有循环（高斯消除和打印）只迭代零次。

删除第二个num_lines声明。

BUG 2：

永远不会初始化'dimension'变量。从逻辑上讲，它应该等于'num_lines'。

BUG 3：

'matrix'变量未正确初始化。你在那里推送'临时'向量，但是只有'num_lines'长度，而不是'num_lines * 2'。

PS：我不能保证没有更多错误。

高斯消元码

1 个答案: