private float coFactor(int c, int r) {
		Matrix3 minor = new Matrix3();
		int i = 0;
		for(int ri = 0;ri < SIZE;ri++) {
			if(ri == c) continue;
			for(int ci = 0;ci < SIZE;ci++) {
				if(ci == r) continue;
				minor.m[i++] = m[ri * 4 + ci];
			}
		}
		if((r + c) % 2 == 0) return minor.determinant();
		else return -minor.determinant();
	}