翻译成中文：BIFPN stands for "Bi-directional Feature Pyramid Network", which is a neural network architecture used for object detection in computer vision. BIFPN was introduced in a paper titled "BiFPN: Efficient Multi-scale Fusion with Repeated Pyramidal Structures" by Tan et al. in 2019. BIFPN is a type of Feature Pyramid Network (FPN) that aims to improve the performance of object detection models by incorporating multi-scale features. BIFPN achieves this by using a repeated pyramidal structure that combines low-level and high-level features through a bidirectional pathway. In BIFPN, the input features are passed through a series of bi-directional nodes that perform top-down and bottom-up feature fusion, resulting in a set of multi-scale features that are robust to variations in object size and scale. The repeated structure of BIFPN helps to ensure that features at all scales are appropriately integrated, while the bidirectional connections help to propagate information between the high-level and low-level features. BIFPN has been shown to be effective in improving the accuracy of object detection models, while also being computationally efficient. As a result, BIFPN has become a popular choice for many state-of-the-art object detection architectures.

BIFPN的全称是“双向特征金字塔网络”，是一种用于计算机视觉中物体检测的神经网络架构，2019年Tan等人发表的论文《BIFPN：带有重复的金字塔结构的高效多尺度融合》中首次提出。BIFPN是一种特征金字塔网络（FPN），旨在通过结合多尺度特征来提高物体检测模型的性能。BIFPN通过使用一个重复的金字塔结构，通过双向通道将低层特征和高层特征融合在一起，从而实现。在BIFPN中，输入特征通过一系列双向节点进行自上而下和自下而上的特征融合，得到一组对物体大小和尺度变化具有鲁棒性的多尺度特征。BIFPN的重复结构有助于确保所有尺度的特征得到适当的集成，而双向连接有助于在高层特征和低层特征之间传播信息。BIFPN已被证明可以有效提高物体检测模型的准确性，同时具有计算效率。因此，BIFPN已成为许多最先进的物体检测架构的首选。

相关问题

使用BFS算法完成以下问题：Angel was caught by the MOLIGPY! He was put in prison by Moligpy. The prison is described as a N * M (N, M <= 200) matrix. There are WALLs, ROADs, and GUARDs in the prison. Angel's friends want to save Angel. Their task is: approach Angel. We assume that "approach Angel" is to get to the position where Angel stays. When there's a guard in the grid, we must kill him (or her?) to move into the grid. We assume that we moving up, down, right, left takes us 1 unit time, and killing a guard takes 1 unit time, too. And we are strong enough to kill all the guards. You have to calculate the minimal time to approach Angel. (We can move only UP, DOWN, LEFT and RIGHT, to the neighbor grid within bound, of course.) Input First line contains two integers stand for N and M. Then N lines follows, every line has M characters. "." stands for road, "a" stands for Angel, and "r" stands for each of Angel's friend. Process to the end of the file. Output For each test case, your program should output a single integer, standing for the minimal time needed. If such a number does no exist, you should output a line containing "Poor ANGEL has to stay in the prison all his life."

解题思路：

这道题可以使用 BFS 算法来解决。首先需要找到起点和终点，并标记出所有的墙和警卫。使用 BFS 算法搜索整个迷宫，每次向四个方向扩展，如果扩展到的位置是墙或者警卫则跳过，否则加入到队列中继续扩展。如果扩展到终点则直接返回步数。最后如果没有找到终点，则说明无法到达，输出 "Poor ANGEL has to stay in the prison all his life."。

具体实现可以按照以下步骤进行：

1. 读入输入数据，找到起点和终点，并标记出所有的墙和警卫。

2. 使用 BFS 算法搜索整个迷宫，每次向四个方向扩展，如果扩展到的位置是墙或者警卫则跳过，否则加入到队列中继续扩展。

3. 如果扩展到终点则直接返回步数。

4. 最后如果没有找到终点，则输出 "Poor ANGEL has to stay in the prison all his life."。

代码实现：

has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. chun

CORS stands for Cross-Origin Resource Sharing, and it is a security mechanism implemented by web browsers to protect users from malicious scripts. When a web page makes a request to a different domain, the browser checks if the server includes the 'Access-Control-Allow-Origin' header in its response. If the header is not present or does not match the origin of the requesting page, the browser blocks the request.

The error message you mentioned, "has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource," indicates that the server you are making a request to does not allow cross-origin requests from your domain. This can happen if the server is not configured properly or intentionally restricts access.

To fix this issue, you have a few options:

1. Modify the server's response headers: If you have control over the server, you can add the 'Access-Control-Allow-Origin' header to the response. This header should include the domain from which you are making the request or use "*" to allow requests from any domain. Here is an example of how to set this header in a server response:

   Access-Control-Allow-Origin: https://your-domain.com

2. Use a proxy server: If you do not have control over the server's configuration or cannot modify it, you can set up a proxy server that acts as an intermediary between your web page and the target server. The proxy server can make the request on behalf of your page, and since the request will be from the same origin as your page, it will not be blocked by CORS restrictions.

3. Utilize JSONP or CORS workaround techniques: JSONP (JSON with Padding) is an older technique that allows cross-origin requests by loading scripts instead of making XMLHttpRequests. However, it has some limitations and potential security risks. Alternatively, some servers may provide specific workarounds or APIs that bypass CORS restrictions. You can check the server's documentation or contact the server owner to see if there are any alternative methods available for making cross-origin requests.

Remember, the specific solution will depend on your server's configuration and the requirements of your application.