qrbksb.cpp

经典算法 主要用于程序员开发 和进行开始学习用

void qrbksb(double a[], int n, double q[], double b[], double x[])
{
	int i,j;
	double sum;
    for (i = 1; i<=n; i++)
	{
        sum = 0.0;
        for (j = 1; j<=n; j++)
		{
            sum = sum + q[(i-1)*n+j] * b[j];
        }
        x[i] = sum;
    }
    for (i = n; i>=1; i--)
	{
        sum = x[i];
        for (j = i + 1; j<=n; j++)
		{
            sum = sum - a[(i-1)*n+j] * x[j];
        }
        if (a[(i-1)*n+i] == 0.0)
		{
			cout<<"a is singular matrix."<<endl;
		}
        x[i] = sum / a[(i-1)*n+i];
    }
}