Lin Zhaoxi was patted heavily on the shoulder.

She turned her head suddenly and Lao Wang looked at her thoughtfully.

"My disciple, are you AFK or is the system delayed in responding? I have been calling you for a long time."

"It could also be a computer crash." Guang interrupted.

"No matter what, the answer is obvious!"

Ah Guang's eyes widened with excitement, while Lao Wang narrowed his eyes, looking like he had won.

Lin Chaoxi looked at them and decided to erase the last sentence he had just written.

She couldn't help but think of what Pei Zhi said when selecting the team members.

She asked Pei Zhi whether he should look for friends who can understand each other when choosing teammates.

Pei Zhi said: Find teammates with the same goals.

Lao Wang's goal is to get the prize, A Guang's goal is to help Lao Wang get the prize, and her goal is to win. Taking all these into consideration, it is obvious which question to choose.

"Ahem." Lao Wang cleared his throat. "According to the convention rules, for the sake of fairness and democracy, our group will use a secret ballot to select the topic."

After Lao Wang finished speaking, he tore off a page of paper from his notebook with a swish sound, randomly tore it into three pieces and handed them to them.

Lin Chaoxi looked at the white paper in front of him, surrounded by the discussions of his classmates who were also participating in the modeling competition.

"Choose this one, choose this one."

"Oh my god, the topic is so accurate. Let's get started quickly. Time is short and the task is heavy."

Such sounds were heard all around her. She took out the pencil case from her schoolbag, and the letter written by Lao Lin was pressed underneath.

She unzipped her pencil case and held the pencil, but she hesitated to write down her choice.

Lao Wang and A Guang had finished writing early, threw the paper ball in the middle of the table, and waited for her.

This is a completely meaningless act, but such a ritual makes these people who make a living by counting numbers feel safe.

Lin Chaoxi's palms were slightly wet. She put down her pencil, looked at Lao Wang and A Guang, and said solemnly, "I want to choose B."

At that time, she had already prepared a long speech to convince the two of them. But Lao Wang said in dissatisfaction: "My disciple, this is too boring!"

Lin Chaoxi felt guilty and wanted to explain, but he heard Lao Wang say, "We want to feel the excitement of the moment of winning the lottery. It's too boring for you to reveal your secrets like this!"

"You are still too young." A Guang shook his head and criticized her.

The two of them opened their paper balls unhappily.

b.

Still b.

It was as if the sun suddenly shone into his heart, and Lin Chaoxi was overjoyed.

But she still asked them seriously: "Teacher, if you don't want aliens, why don't you choose a question that you have a better grasp of?"

Lao Wang picked up a ballpoint pen and tapped her head with it: "Keep your voice down. Do you know what it means that walls have ears?"

Lin Chaoxi lowered his voice and asked the question again.

"Are you stupid? Everyone would choose question A, but we chose question B. Isn't it a different approach that would increase our chances of winning?" Lao Wang's voice was as soft as a mosquito's hum, like a thief's.

Lin Zhaoxi nodded.

"Muggles will definitely choose easy questions, but we are different, we need challenges!" A Guang shouted excitedly.

Lin Chaoxi continued to nod.

"That's settled then!" said Lao Wang happily.

——

There were dozens of machines running in the computer room, and dozens of students were discussing enthusiastically. No matter how low the air conditioner was turned, it couldn't suppress the lively atmosphere.

After the initial excitement and excitement, Lin Chaoxi quickly calmed down.

Although this problem of chasing a fugitive is very similar to the problem of predicting Lao Lin’s car accident, they are still different.

According to the strategy they had prepared, the three of them began to carefully review the questions and express their opinions. This is commonly known as brainstorming.

Lao Wang started to preside over the meeting in the old cadre mode again: "Everyone, please share your opinions. This question is still very difficult."

Ah Guang opened the document in the appendix, which contained densely packed call records: "It's quite sinister. Among these alarms, there must be false alarms and real alarms. We need to distinguish them."

"How to distinguish?" Lao Wang asked.

"Bayesian network," Lin Zhaoxi said.

"Wow!" Lao Wang took a deep breath, "Disciple, you may be young, but you have such a big mouth!"

"We can assign a probability to each sighting. The greater the probability, the more likely it is to happen." Lin Chaoxi said, taking the draft paper. She first drew a simple map on it and then marked it with a grid.

"Divide the map into grids of equal size, with n and e representing their longitude and latitude, t representing time, and p(n, e, t) representing the probability that the fugitive will appear at a certain location at a certain time."

Lao Wang and A Guang frowned in deep thought.

Lao Wang: "And update it continuously in chronological order?"

Lin Zhaoxi nodded.

"I think it's possible," said Guang. "First, assign different prior probabilities to each square, and use the likelihood of the witnessed event to update the posterior probability p(i, j) of each small square."

"Yes, in fact, it is based on eyewitness reports, combined with traffic conditions, road and bridge structures, and historical data, and constantly assigns new values ​​to each square."

"For example, this one and this one." Lin Zhaoxi pointed to two reports in the police report record. "One shows that the fugitive is in the east of the city, and the other shows that he is in the west of the city. But if the report at the previous moment also shows that the suspect is in the east of the city, then the report in the west of the city is obviously less credible."

"That's why, during time t+1, the sightings near this road in the west of the city were valued higher," Lao Wang continued.

"Um."

"So we need to use Bayesian networks?" Lao Wang said, "We can use Bayesian theorem repeatedly, and as more and more evidence is collected, we can continuously update the posterior probability to compensate for the bias caused by subjective judgment?"

"Yes." Lin Zhaoxi said, "That is to say, we can consider all possible locations where the fugitive may appear at each time point at the same time, and obtain a probability distribution map. The values ​​on this map are constantly updated..."

"It's you!" Old Wang was shocked. "Your thinking is too strange, isn't it? Let me open your brain and see!"

"I'm smarter?" Lin Chaoxi quickly dodged.

Ah Guang had already written a lot of drafts on paper. Suddenly he looked up and said, "Damn, I can't refute it. You are really smart."

He said.

——

Lin Chaoxi was actually very ashamed, as this was the idea she had come up with after studying the car accident problem in depth for a long time. However, Lao Wang and A Guang seemed to understand it immediately, and the following discussion became the main focus of Lao Wang and A Guang.

Generally speaking, participating teams in modeling competitions must have a division of labor. One person is responsible for modeling; one person is the main author of the paper; and the last person is responsible for programming, data generation and verification.

According to the plan they had made in advance, Lao Wang was responsible for modeling, A Guang was responsible for programming, and she did more basic writing work, constructing the thesis framework and writing the thesis.

but……

"Why do you think Python is better? Matlab is still the first tool for scientific computing. It is the best tool for mathematical modeling and has many toolboxes and countless mature modules that can be used," said Guang.

"But there are also many third-party modules in Python. The numpy module allows Python to directly process large matrices like Matlab, the scipy module encapsulates a large number of algorithms, and the matplotlib module allows Python to draw a large number of function graphs. In short, Python can replace most of the functions in Matlab, and has some advantages that Matlab cannot replace."

"Python is good, but I haven't studied it in depth. I'm good with Matlab." A Guang thought for a moment and continued, "I haven't verified what you said, so I'm still skeptical whether it's really useful."

Lin Zhaoxi: "Please believe me."

"But since I'm in charge of programming, shouldn't you trust me?" said Guang.

Lin Chaoxi didn't know how to refute it. After thinking for a while, she asked, "What if I insist?"

"Then you will be responsible for programming."

A Guang was outspoken and said this directly, but Lin Chaoxi was stunned.

According to the prior arrangement, all her preparations were related to writing the paper, and she confidently handed over the programming issues to Guang. Now Guang's "then you do it" overturned all her previous preparations.

But from Guang's point of view, if he was in charge of programming, they should trust his judgment, which he did.

But the problem is that she only knows a little more than them in this area, and she trusts her own judgment more.

After a heated discussion, the classroom became much quieter. Like them, many groups encountered many inevitable disputes after experiencing the initial excitement and starting to solve the problem.

Small-scale arguments broke out in various groups, some over topic selection, some over ideas. Of course, there were also groups like them that started new debates due to changes in division of labor.

After they said some negative words to each other, the atmosphere in the whole classroom became cold.

Time flies and it's already noon.

At this time, Jie Ran came over again. He glanced at the situation of each group in the computer room and seemed to know everything.

He walked up to the podium slowly, clapped his hands, and said with a smile: "Excuse me, aren't you hungry? Do you want to go get some instant noodles?"

There was total silence all around; no one was talking.

"Then let's go to the cafeteria and have something to eat." Xie Ran looked full and satisfied. "The chicken legs in the cafeteria are pretty good."

Still no response.

"Let's go out for a walk." A clear and calm voice sounded from the last corner of the classroom.

Pei Zhi, who had been sitting at the end of the classroom, stood up at some point. Finally, there was a small commotion in the computer room other than the operation of the computers.

“We’re still discussing it.”

"Time is so tight, let's skip dinner."

"Senior..."

Unlike the attitude of He Jieran who tried to persuade others with kind words, Pei Zhi was unexpectedly strong. He did not say anything, but just stood there, which made people consider his suggestions.

Lin Chaoxi took a deep breath and understood Pei Zhi's intention. She stood up first, patted Lao Wang on the shoulder, and said to A Guang: "Let's go, let's go eat."

Lao Wang was stunned for a moment: "Disciple, are all women as fickle as you?"

Lin Zhaoxi: "Am I a woman now?"

"I'm sorry, I forgot." Lao Wang apologized immediately.

Lin Chaoxi took the lead and walked out of the gloomy computer room with the others.

When I came out into the open air and felt the spring breeze blowing on my face, my stress immediately dissipated a lot.

Walking down the stairs one step at a time, Lin Chaoxi felt that she was really hungry. She stepped down the last step, holding onto the railing, her legs weak.

Lao Wang and A Guang were walking in front and turned to look at her.

"What's wrong with you?" A Guang asked.

Lin Zhaoxi covered his stomach: "I'm hungry."

"So sudden! You women are really fickle!" said A Guang.

Lin Chaoxi looked at the boy not far away. In the sunlight, he had an innocent look on his face.

In fact, there was nothing to worry about. The choice before her was very simple. Either A Guang did the programming or she did it.

She said to Guang, "I am familiar with Python. I can write the program if you are willing to do so."

Ah Guang was also very straightforward: "Okay, you can teach me too, let's study together and see if Matlab can complement Python."

"What about the thesis? Who will do it?" Old Wang was shocked.

"Since we need to look up information, Lin Chaoxi and I will do it together. Let's write the summary and framework together first."

"When did you become so united?"

Lin Chaoxi did not answer Lao Wang's question, but said to A Guang: "When it comes to writing the program, I can write it first and you can check it later. For the thesis, you can write the outline first, and I will correct some details, such as font format, etc."

"Can."

"Then I am only responsible for building a mathematical model to solve the problem?" Suddenly, Lao Wang seemed to have figured something out. His expression was tangled. He smacked his lips and said, "I... why do I feel like I'm being led to lie down?"

Lin Zhaoxi smiled: "No, no, no, we all rely on Teacher Wang."