Gaussian Elimination program

This is a discussion on Gaussian Elimination program within the C++ Programming forums, part of the General Programming Boards category; I'm not sure what's wrong, i get the wrong the answers for x, i should be getting: x0=1 x1=-1 x2=1 ...

  1. #1
    Registered User
    Join Date
    Mar 2011
    Posts
    4

    Gaussian Elimination program

    I'm not sure what's wrong, i get the wrong the answers for x, i should be getting:
    x0=1
    x1=-1
    x2=1

    Code:
    int main()
    {
    
    	int n = 3, i = 0, j = 0, k = 0;
    	double m = 0;
    
    	double *b;
    	b = new double[n];
    	b[0]=0; b[1]=3; b[2]=2;
    
    	double *x;
    	x = new double[n];
    	double **A;
    	A = new double *[n];
    	for(int i=0; i<n; i++)
    		A[i] = new double [n];
    	A[0][0]=1; A[0][1]=2; A[0][2]=1; 
    	A[1][0]=2; A[1][1]=2; A[1][2]=3; 
    	A[2][0]=-1; A[2][1]=-3; A[2][2]=0;
    
    	for (int k=0; k<=n-2; k++)
    	{
    		for (int i=k+1; i<=n-1;i++)
    		{
    			double m = A[i][j]/A[k][k];
    			for (int j=k; j<=n-1; j++)
    				A[i][j] = A[i][j] - m*A[k][j];
    			b[i] = b[i] - m*b[k];
    		}
    	}
    	x[n-1] = b[n-1]/A[n-1][n-1];
    	for (k=n-2; k>=0; k--)
    	{
    		x[k]=0;
    		for (j=k+1; j<=n-1; j++)
    			x[k] = x[k] + A[k][j] * x[j];
    		x[k] = (b[k] - x[k])/A[k][k];
    	}
    	cout << x[1];
    	system ("pause");
    	return 0;
    }

  2. #2
    Registered User
    Join Date
    Jun 2005
    Posts
    6,295
    You've probably confused yourself by having multiple variables named i,j, and k in different scopes.
    Right 98% of the time, and don't care about the other 3%.

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