作业答案有bug

[langziwuqing]

4 卷积神经网络/Week3 目标检测/4.3 目标检测/Car detection for Autonomous Driving/Autonomous driving application-Car detection-v1-answer.ipynb，计算iou的函数，此段代码有bug：
xi1 = max(box1[0], box2[0])
yi1 = max(box1[1], box2[1])
xi2 = min(box1[2], box2[2])
yi2 = min(box1[3], box2[3])
inter_area = (yi2 - yi1) * (xi2 - xi1)
当两个框没有重叠时，yi2 - yi1和xi2 - xi1的值都是负数，inter_area应该是0，所以应该这么写：
xi1 = max(box1[0], box2[0])
yi1 = max(box1[1], box2[1])
xi2 = min(box1[2], box2[2])
yi2 = min(box1[3], box2[3])
if (yi2 - yi1 < 0) or (xi2 - xi1 < 0):
inter_area = 0
else:
inter_area = (yi2 - yi1) * (xi2 - xi1)