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#include <iostream>
using namespace std;
 
 
inline void OutputMatrix(vector< vector<double> > matrix, int nx, int ny)
{
	for(int i = 0; i < nx; ++i){
		for(int j = 0; j < ny; ++j){
			cout << matrix[i][j] << (j == ny-1 ? "" : " ");
		}
		cout << endl;
	}
}
 
 
 
int main(){
 
    int n=4;
    vector<vector<double>> A={
        {9,2,0,0,2},
        {-2,4,-1,0,0},
        {0,-1,5,-2,1},
        {0,0,-2,6,9}
    };
 
 
    for(int k = 0; k < n-1; ++k){
		double akk = A[k][k];
		for(int i = k+1; i < n; ++i){
			double aik = A[i][k];
			for(int j = k; j < n+1; ++j){ // 確認のため左下要素が0になるようにj=kとしたが，実際にはj=k+1でよい
				A[i][j] = A[i][j]-aik*(A[k][j]/akk);
			}
		}
		cout << "k = " << k << endl;
		OutputMatrix(A, n, n+1);
		cout << endl;
	}
 
	// 後退代入(back substitution)
	//  - x_nの解はb_n/a_nn，x_nをさらにn-1行の式に代入することでx_(n-1)を求める．
	//  - この作業を1行目まで続けることですべての解を得る．
	A[n-1][n] = A[n-1][n]/A[n-1][n-1];
	for(int i = n-2; i >= 0; --i){
		double ax = 0.0;
		for(int j = i+1; j < n; ++j){
			ax += A[i][j]*A[j][n];
		}
		A[i][n] = (A[i][n]-ax)/A[i][i];
 
		cout << "i = " << i << endl;
		OutputMatrix(A, n, n+1);
		cout << endl;
	}
 
    return 0;
}
 
 
 
 

prog.cpp:5:26: error: variable or field ‘OutputMatrix’ declared void
 inline void OutputMatrix(vector< vector<double> > matrix, int nx, int ny)
                          ^~~~~~
prog.cpp:5:26: error: ‘vector’ was not declared in this scope
prog.cpp:5:26: note: ‘std::vector’ is defined in header ‘<vector>’; did you forget to ‘#include <vector>’?
prog.cpp:2:1:
+#include <vector>
 using namespace std;
prog.cpp:5:26:
 inline void OutputMatrix(vector< vector<double> > matrix, int nx, int ny)
                          ^~~~~~
prog.cpp:5:34: error: ‘vector’ was not declared in this scope
 inline void OutputMatrix(vector< vector<double> > matrix, int nx, int ny)
                                  ^~~~~~
prog.cpp:5:34: note: ‘std::vector’ is defined in header ‘<vector>’; did you forget to ‘#include <vector>’?
prog.cpp:5:41: error: expected primary-expression before ‘double’
 inline void OutputMatrix(vector< vector<double> > matrix, int nx, int ny)
                                         ^~~~~~
prog.cpp:5:59: error: expected primary-expression before ‘int’
 inline void OutputMatrix(vector< vector<double> > matrix, int nx, int ny)
                                                           ^~~
prog.cpp:5:67: error: expected primary-expression before ‘int’
 inline void OutputMatrix(vector< vector<double> > matrix, int nx, int ny)
                                                                   ^~~
prog.cpp: In function ‘int main()’:
prog.cpp:20:5: error: ‘vector’ was not declared in this scope
     vector<vector<double>> A={
     ^~~~~~
prog.cpp:20:5: note: ‘std::vector’ is defined in header ‘<vector>’; did you forget to ‘#include <vector>’?
prog.cpp:20:19: error: expected primary-expression before ‘double’
     vector<vector<double>> A={
                   ^~~~~~
prog.cpp:29:16: error: ‘A’ was not declared in this scope
   double akk = A[k][k];
                ^
prog.cpp:37:3: error: ‘OutputMatrix’ was not declared in this scope
   OutputMatrix(A, n, n+1);
   ^~~~~~~~~~~~
prog.cpp:44:2: error: ‘A’ was not declared in this scope
  A[n-1][n] = A[n-1][n]/A[n-1][n-1];
  ^
prog.cpp:53:3: error: ‘OutputMatrix’ was not declared in this scope
   OutputMatrix(A, n, n+1);
   ^~~~~~~~~~~~

Standard output is empty