typedef double Matrix[N][N];void gauss_elimination(Matrix A,int n){    int i,j,k,r;    for(i=0;i<n;i++)    {        //选一行r并与i行交换        r = i;        for(j=i+1;j<n;j++)            if(fabs(A[j][i]) > fabs(A[r][i]))                r = j;        if(r != i)        {            for(j=0;j<=n;j++)                swap(A[r][j],A[i][j]);        }        //与第i+1~n行进行消元        for(k=i+1;k<n;k++)        {            double f = A[k][i]/A[i][i];  //为了让A[k][i] = 0,第i行乘以的倍数            for(j=i;j<=n;j++)                A[k][j] -= f*A[i][j];        }    }    //回代    for(i=n-1;i>=0;i--)    {        for(j=i+1;j<n;j++)            A[i][n] -= A[j][n]*A[i][j];        A[i][n] /= A[i][i];    }}