Early morning, by the river.
Lin Chaoxi scattered the scraps of paper into the stream. Not far away, Chen Zhu waved at her.
Lin Chaoxi was startled.
"Why do you just throw garbage into the river?" Chen Zhu walked towards her, biting a bun.
“Don’t tell the teacher.” Lin Chaoxi mumbled something nonsense, took the bag handed to him by Chen Zhu, took out a bun from it, and took a bite.
Chen Zhu looked around and asked, "Why hasn't Pei Zhi come yet?"
"He's busy."
Chen Zhu was stunned: "What happened to him?"
"Why do you think something happened to him?" Lin Zhaoxi walked onto the bridge.
"When has Pei Zhi ever been late?"
Lin Zhaoxi thought that Brother Pei always seemed to be so meticulous: "Something big happened, but there is no way to solve it."
If it was Comrade Lao Lu, he would probably pull her aside and ask what was going on and why she didn't go help Pei Zhi and so on.
But Chen Zhu was very straightforward and just said, "Oh, call me if you need anything."
Lin Zhaoxi patted Chen Zhu on the shoulder: "Of course I need you."
——
Chen Zhu's home, small garage.
Lin Chaoxi turned on the switch, and the light shone on the chairs where she and Pei Zhi often sat.
The water cup she had used on the table was clean and bright. When she left last time, Pei Zhi even washed the cup for her.
Chen Zhu had already sat down and turned on the computer. The machine was buzzing. Lin Chaoxi calmed down and turned on the monitor.
About two weeks ago, she completed the prediction process, but to test whether the process is effective, she still needs to predict specific events.
But choosing what to do becomes a difficult issue.
Lin Chaoxi originally wanted to ask Chen Zhu's father to find a hit-and-run case, and have the program calculate the best arrest location and arrange police force to handle it.
Although it sounds simple, Lin Chaoxi himself knows that this is not a resource that a high school student is allowed to mobilize for extracurricular activities.
But she tried to ask anyway.
After hearing what she said, Chen Zhu's father rejected her proposal. The adults all thought that students should focus on their studies.
"You only need to tell us the time and location of the escape, and some basic surveillance data, nothing else."
"Chao Xi, uncle knows you have ideas, but this is China. It's not as open as foreign education. Many things are not practical."
What this probably means is that leaders will not allow high school students to participate in catching hit-and-runs, even in the name of extracurricular practice.
Lin Chaoxi really wants to say that before I did this, I also felt that many things seemed like fairy tales, but after doing it, I found that they were not as incredible as I imagined.
But before she could explain, there was a sudden commotion in the new village.
Several aunties in the garden were making a lot of noise. Some shouted, "Oh, hurry up and find him," while others shouted, "Call 110" and so on.
A neighbor knew that Chen's father was a traffic policeman, so he ran to their garage and shouted, "Hey, Old Chen, is the public security situation a problem now? Another car has been stolen!"
Lin Chaoxi listened for a while and found out that there have been many thefts of electric bikes in the community recently.
The new village is too old, security is non-existent, and there is not even a wall, which leads to the thief gangs favoring the Ai Min community.
Pei Zhi was beside her at that time. She and Pei Zhi looked at each other and came up with new plans.
She stopped focusing on the hit-and-run incident and started investigating the theft of an electric bike in Ai Min New Village.
Statistics include the time and frequency of thefts, nearby traffic data, the speed of electric vehicles, and the places where thieves often sell stolen goods.
The purpose is to catch thieves.
To do this, they changed some of the forecast parameters and re-tested the program.
The prediction results based on the frequency of crime occurrences point to Sunday morning as the stalking is common during this time of year when commuters generally take a break and there are few people in the new village, so the number of electric bike thefts is high.
Originally they were almost ready, except for waiting, but Pei Zhi was not there, so many arrangements had to be made again.
"What should we do?" Chen Zhu asked.
"Then you can only sit in front of the computer and look at the results. I'm leaving."
"You have to adapt to the situation and change parameters. I can't do any of that. I'll have to go." Chen Zhu paused. "Besides, how can you, a girl, catch a thief?"
"Uh...sometimes I forget I'm a girl."
Lin Chaoxi said very honestly.
——
The time was 6:01 am on Sunday morning, and the wait was long.
Lin Chaoxi slept no more than 4 hours yesterday. After sitting in front of the computer for a while, he felt sleepy.
She had just had a cup of instant coffee, but it didn't help at all. As a last resort, she asked Chen Zhu if he had any tea.
"It's in the canteen. Go ahead and bring me a pack of chewing gum," said Chen Zhu.
Lin Chaoxi walked out of the garage, the sky was still gray. She stretched her back and saw Chen Zhu's father coming down the stairs. He waved from a distance and greeted Old Chen.
Chen Jianguo was yawning, and seeing this, he quickly put away his tired expression and said, "Chaoxi, why did you come so early?"
"We are stalking the guys who stole the electric bikes." Lin Chaoxi said directly.
Old Chen was stunned for a moment, looking at the girl's righteous face, he felt helpless: "You guys..."
He and Lin Chaoxi walked towards the canteen together.
The girl ordered a pack of "Mankouxiang" tea for five yuan. When Chen Jianguo was about to pay, he saw the pack of tea leaves and suddenly said, "What kind of tea do you want to drink at such a young age?"
Lin Zhaoxi yawned, his eyes were bloodshot, but his gaze was still soft and bright: "Uncle, I'm really sleepy."
For some reason, Chen Jianguo suddenly felt that he had gone too far.
——
Early morning, small garage.
Lin Chaoxi unpacked the tea leaves and brewed a full cup of strong tea. She placed the cup next to the computer and took out a book on algorithms and started reading it.
Chen Jianguo followed the girl into the room and was attracted by the computer screen at first sight.
Although he didn't understand what it was, it seemed to be just a simple program with a lot of codes. It seemed to be constantly performing calculations and would produce some new results.
The girl looked up at the screen from time to time, tapped the keyboard briefly and skillfully, and the program started running again.
Chen Jianguo's eyes widened.
Suddenly, the garage fell silent. Chen Jianguo looked up and saw his son looking at him with a look that said, "Why aren't you leaving yet?"
Chen Jianguo coughed and said, "Chaoxi, is there anything else you need uncle's help with?"
As soon as he finished speaking, Lin Zhaoxi suddenly raised his head and gave him a sly smile: "Great, then I'll trouble you, uncle."
Just like this, another half hour passed.
Chen Jianguo sat in his family's small garage, watching Lin Chaoxi drink three cups of water and listening to the sound of his son typing on the keyboard and turning pages.
It was getting a little lively outside the garage. Old people were coming out to buy groceries, and sleepless children were running around in the yard.
A quilt was hung on the horizontal bar in the new village to dry in the sun. Chen Jianguo felt that at this time, it was unlikely that a thief would come out to steal the electric bikes.
He moved around, looking at the children on both sides who were concentrating on their studies, and finally couldn't help asking: "Are you sure that a thief will come to steal your car this morning?"
"Well, I can't say for sure, I can only say that it is most likely today."
"How can this be calculated?"
"Human behavior may seem chaotic, but it has internal patterns." Lin Chaoxi paused, "Especially criminal behavior. We think they happen independently, but in fact, they are not. Events are temporally related."
Lin Zhaoxi picked up a pen and wrote a long formula on the paper: "Using the Hawkes process, we can statistically model the time and frequency of battery bike thefts, and then describe them with exact numbers and formulas."
"Huo, what process?" Chen Jianguo was confused, but the girl suddenly looked outside the garage.
The small-scale commotion started from far away.
At first, no one knew which family was looking for something, and then a couple started arguing and blaming each other. Soon, the whole community knew that Mr. Wang from Building 7 had left his car in the garage locked in order to steal the battery from the corridor, so his car was stolen.
Chen Zhu stood up and walked out with his notebook and mobile phone. Lin Chaoxi, on the other hand, sat in front of the computer, closed the book, and started looking at the screen.
Chen Jianguo quickly ran out after his son.
When Chen Zhu arrived at the scene, he acted like a traffic police officer investigating a traffic accident. He began to inquire about the brand and model of the stolen electric bike.
"How would we know the model and brand of this broken car? We bought it a long time ago," said the woman.
"How many years?" Chen Zhu asked again, "Have you changed the battery?"
Chen Jianguo saw the woman give his son a strange look and couldn't help but ask, "What does the lost car look like? Do you have a photo?"
The woman muttered to herself what photos of the broken electric bike there were, while she started flipping through her phone.
Soon, she found a photo of her and her son riding a bicycle.
At this moment, a howl was heard from Building 8 next to Building 7: "You unscrupulous thieves! I just replaced the battery the day before yesterday!!!"
Chen Zhu put away his notes and went back to Building 8. It seemed that the thief not only stole the battery car from Lao Wang's family, but also stole the battery from Lao Zhang's family.
Without the battery, the electric bike is just an iron frame with a big hole in the middle, which looks very sneaky.
Chen Zhu carefully looked at the model of the electric bike, took two photos, and ran back to the garage. Chen Jianguo followed him.
In the garage, Lin Chaoxi had already opened a huge Excel document, which contained dense electric vehicle data, including vehicle model, driving speed, etc.
Chen Zhu showed the photos of the scene, and the two children studied them for a while and determined several values.
Next, he saw them pull up the prepared road map, which showed a lot of densely packed traffic lights and roads, with different values assigned to them, making it look chaotic.
Lin Chaoxi and Chen Zhu studied it for a while, determined a few routes, and began to type code into the program.
Chen Jianguo was puzzled again: "But how do you know when the thief stole the car? Does this count?"
“It’s hard to calculate, so we installed surveillance cameras in all directions of the community.”
The girl's voice was nonchalant, and she pointed to Chen Zhu's position. Chen Jianguo ran over and saw his son dragging and dropping the timeline of the surveillance video, and he almost choked on his own saliva.
These kids are really going too far, installing surveillance cameras just to catch thieves!
"There is also a route. How did you determine it?" Chen Jianguo held back his surprise and continued to ask.
"We have investigated a lot of news and the used car recycling market. After stealing a car, thieves have two ways to dispose of it. The first is to sell it directly, and the second is to change the appearance of the car and then sell it."
Chen Zhu said confidently, "No matter what method is used to sell the stolen vehicles, it takes a certain amount of time to find the selling point from the theft point. Constrained optimization can be used to find the best selling point for the stolen electric vehicles in our Aimin community."
"So...you guys did all this?" Chen Jianguo was shocked.
"She did it." Chen Zhu pointed at the girl who took a big sip of tea in front of the computer.
Lin Chaoxi raised his head, tapped his forehead with his index and middle fingers, and greeted him with a smile.
Chen Jianguo didn't know what constrained optimization meant. He only saw the simple program on the monitor start to calculate quickly, with line of code pouring out, and then suddenly stop at a certain point in time.
A pop-up window appears.
That was a map of their area, with three red circles on it, representing three outcomes.
Hongxing Road 6:41-6:44
Simin Road 6:45-6:47
Heping Street 6:51-6:55
The time on the lower right corner of the computer was 6:45. It was basically too late to reach Hongxing Road and Simin Road. It would take them at least seven or eight minutes to get to Heping Street by bike.
"Excuse me, uncle." The girl turned around, her eyes bright and firm.
Chen Jianguo turned around and ran without saying a word.
He got on the motorcycle, put on his helmet, started the engine, and the police motorcycle rushed forward.
The strong wind blew past his ears and the street scene receded. Chen Jianguo felt that at his age, he had not been this crazy for a long time.
If we can really catch it, it would be amazing.
Chen Jianguo thought excitedly.
——
Heping Street.
The motorcycle braked suddenly, making a sharp sound. Chen Jianguo jumped off the motorcycle and looked at his watch. It was still in time.
The time was 6:52, and he began to observe nervously.
It was late autumn and early winter, and it was still dark after six o'clock.
Heping Street is not a main road and there are even fewer pedestrians. If someone riding an electric scooter or a car with a battery passes by, it will be easily discovered.
He stared with bated breath, waiting.
An old man riding a bicycle, an old lady buying groceries, a young man with his girlfriend...
——
Five minutes passed.
Ten minutes passed.
The sky was getting brighter and brighter, gradually changing from indigo to transparent. The intersection was getting busier and busier, but Chen Jianguo was getting more and more...
Finally, his cell phone rang.
"Uncle Chen." The girl on the other end of the phone said calmly, "Didn't you see the thief?"
"I didn't see it." Chen Jianguo paused and looked towards the four-way intersection. "Maybe my uncle didn't get there in time."
"It's not uncle's fault, it's just that the program is not accurate enough."
Chen Jianguo held up his phone, and could almost imagine Lin Chaoxi's frustrated face. He said quickly, "Don't be discouraged. Uncle thinks you are already very good."
"Is uncle comforting me?"
"It's not consolation, it's encouragement..."
"Uncle, can you take me to the traffic police detachment to see the surveillance at this time and continue to encourage me?"
The girl on the other end of the phone asked this.
——
The little girl's voice was crisp, without any hint of sadness, but precisely because of this, Chen Jianguo couldn't refuse.
He brought his son and daughter into the team and checked the video. When his colleagues teased him about having both a son and a daughter, he made up an excuse to get away with it.
"Mr. Chen, which time period do you want to watch?"
Lin Chaoxi didn't say anything. Chen Jianguo stood behind the display screen and reported several intersections and times that he had just memorized.
After he said this, he suddenly realized that the results calculated by the program were all about avoiding surveillance and passing through the alleys to the intersections. It was really amazing.
As the timeline is dragged, the monitor starts to display the scene of Heping Street.
Chen Jianguo was still thinking, if the thief really did not leave through Heping Street, he would continue to investigate the situation at the remaining two points.
While he was still making plans, a pink electric car slowly drove past the intersection.
The left pedal was off and there was a rat ball on the body of the car.
It turned out to be the car that was stolen from Lao Wang’s house. The surveillance video showed the time was 6:51:03 seconds. About 1 minute later, he appeared on a motorcycle.
"Oh, it's just this close!" Chen Jianguo shouted.
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