求矩陣行列式

double det() {
	for (int i = 1; i < n; i++) {
		for (int j = 0; j < i; j++)
			if (A[i][j] != 0) {
				for (int k = j + 1; k < n; k++)
					A[i][k] -= (A[j][k] * A[i][j] / A[j][j]);
				A[i][j] = 0;
			}
	}
	double ans = 1;
	for (int i = 0; i < m * m - 1; i++)
		ans *= A[i][i];
	return ans;
}