temperature
As autumn deepened, the lab's air conditioning was finally turned down. Luo Yan stared at the "Recognition Failed" message box flashing repeatedly on the screen, her fingertips hovering over the keyboard for a long time, not even noticing the stray hairs from the back of her neck brushing against her cheek.
“The 17th set of data is wrong again.” She muttered to herself, pulling the video progress bar back to the starting point. In the video, a boy wearing glasses was making a backhand shot. His knee bend angle and body rotation were all within the standard range, but the system stubbornly judged it as an “incorrect action.” The red warning box was like a glaring patch stuck in the center of the screen.
This is the third time this week that a similar problem has occurred. Luo Yan pulled up the algorithm log, and lines of green code floated before her eyes, finally stopping at the "feature extraction module"—the problem lay in the judgment of "wrist relaxation." The system relied on data from the accelerometer, but ignored a more subtle signal: the change in the angle between the racket and the forearm when the wrist rotated.
She rubbed her throbbing temples, recalling Qi Sheng's words on the list: "A novice's mistakes are often hidden in 'seemingly standard' actions." Her fingertip hovered over the mouse for a moment, then she finally opened the email interface. As she entered that familiar email address into the recipient field, her heart skipped a beat.
"Regarding the issue of abnormal recognition of backhand movements, I would like to ask a few questions about the details." She wrote concisely, attaching the error video and log screenshots. Before sending it, she hesitated for two seconds and deleted the three words "thank you for your help" at the end.
Less than ten minutes after the email was sent, my phone vibrated. It wasn't a reply to the email, but a text message from Qi Sheng: "Are you in the lab? I'll come over."
As Luo Yan stood up, phone in hand, her knee bumped against the table leg with a soft thud. She bent over, rubbing her knee, but her ears burned uncontrollably—this was the first time in over a year that he had taken the initiative to see her, not in a crowded conference room, but in their private lab.
Fifteen minutes later, there was a knock on the door. Luo Yan opened it and saw Qi Sheng standing in the hallway, wearing a light-colored shirt. He was holding a black folder. Seeing her rubbing her knee, he frowned slightly: "Did you bump into something?"
"It's nothing." Luo Yan stepped aside to let him in, and smelled a hint of osmanthus fragrance mixed with the mint scent on him—it must have picked up from the osmanthus tree in front of the library when she passed by.
Qi Sheng walked to the screen, but instead of immediately watching the video, he noticed the mug on the corner of the table. The coffee in the mug had gone cold, and a layer of light brown stains had formed on the inside; she had forgotten to change it in her busyness. His gaze lingered on the mug for half a second before turning to ask, "Which set of data?"
“Group 17.” Luo Yan pointed to the screen. “Look, the motion parameters are all within the standard range, but the system is making a mistake.”
He didn't speak, pulled up a chair next to him, and sat down, placing the folder on his lap. On his exposed wrist, the hands of his watch pointed to 4:30 PM. As the video started playing, he took a pen out of his pocket.
"Pause." He spoke at 0 minutes and 12 seconds into the video, his voice lower than usual. Luo Yan pressed the pause button, and the image froze at the moment the boy's wrist turned.
Qi Sheng tapped the screen with the tip of his pen: "Here, the angle between the racket and the forearm is 170 degrees, while the standard value should be 180 degrees."
"A 10-degree error is within the system's allowable range of 15 degrees." Luo Yan pulled up the parameter table. "Logically, it shouldn't be considered an error."
“For professional players, 10 degrees is nothing.” He twirled the pen in his hand, the metal pen body reflecting a faint light under the light. “But for beginners, 10 degrees hides tension—their wrists subconsciously tense up the moment they exert force, but they cover up this detail with the range of their body rotation.”
Luo Yan was stunned. The system's sensors did not detect this change, because the acceleration data showed "wrist relaxed," but the white knuckles of the boy's clenched fist in the video did indeed conceal a subtle tension.
“How does the algorithm identify this kind of ‘implicit tension’?” she asked, her fingertips unconsciously tapping the table.
Qi Sheng didn't answer directly. Instead, he pulled out a piece of paper from the folder, on which was a detailed breakdown of the movements. It wasn't printed; it was hand-drawn, marked with different colored pens: red for "explicit errors" (such as insufficient knee flexion), and blue for "implicit errors" (such as slight wrist tremors). Under the section on "wrist relaxation," he wrote in blue pen: "Look at the reflective point on the racket—when relaxed, the reflective point will move naturally with the wrist rotation; when tense, the reflective point will suddenly 'jump'."
Luo Yan paused in her breathing.
This was a technique she used to employ when drawing portrait sketches. Back then, she could never quite capture the changes in a person's eyes, so Song Tian taught her to "look at the reflection in the pupils," saying that "emotions are hidden in the movement of light." She never imagined that years later, she would see a similar logic in Qi Sheng's motion analysis diagrams.
“We can add a ‘reflection point tracking’ module to the algorithm.” Qi Sheng’s voice brought her back to reality. “Using image processing to identify highlights on the racket, combined with acceleration data, will greatly improve the accuracy.”
When he spoke, his soft hair covered his forehead, and Luo Yan could only see his straight nose and a small mole on the tip of his nose.
"Thank you." Luo Yan lowered her head and opened the code editor. "I'll give it a try."
Qi Sheng didn't leave. He sat on the chair next to her, flipping through folders, occasionally glancing up at her screen. The lab was quiet, save for the sounds of keyboard clicks and the rustling of his pages, like a slow duet. The setting sun streamed in through the window, casting a diamond-shaped patch of light on his knees, swaying gently with each page turn.
By 6 p.m., the algorithm had finally passed the test. The recognition result for the 17th set of data turned green as "correct". Luo Yan breathed a sigh of relief and turned to tell Qi Sheng, only to find that he had fallen asleep leaning against the back of his chair.
A few stray hairs slid down his forehead, revealing a faint mark on his forehead, likely from years of looking down at documents. His long eyelashes cast soft shadows under his eyes, and his usually taut jawline was relaxed, his lips slightly downturned, as if he were having an unhappy dream.
She rarely saw him so relaxed. In her memory, Qi Sheng was still the cold, snowy figure from last winter, like a piece of candy with a hard shell, making one forget that he also had moments of exhaustion.
The phone on the table vibrated; it was a message from Zhang Qi: "We're having dinner tonight, are you coming?" Luo Yan replied, "No, I'm working overtime," afraid the ringing would wake him.
She got up and went to the break room to make a cup of hot milk. When she returned, Qi Sheng was already awake, rubbing his eyes. He paused, stunned, when he saw the milk in her hand.
"It's freshly brewed." Luo Yan placed the cup in front of him, her fingertips accidentally touching the cup's rim, causing her to recoil from the heat.
"Thank you." He picked up the cup, the steam from the milk clinging to his fingertips, leaving a faint wisp of mist on the cup's surface. He took a sip, his brow relaxing slightly.
Luo Yan lowered her head and typed on the keyboard, "The algorithm is fixed, do you want to take a look?"
As he leaned closer to look at the screen, the scent of mint mixed with milk wafted over, brushing against her ear. Luo Yan's fingers stiffened; she felt his shoulder was very close to hers, close enough to see even the osmanthus petal stuck to his shirt.
"Very accurate." Qi Sheng's voice carried a hint of amusement after reading the test results, a gentle tone that Luo Yan had never heard before. "Faster than I expected."
"Your suggestion was helpful." Luo Yan's voice was very soft, as if afraid of disturbing this rare peace.
He didn't reply, picked up the folder and stood up: "Then I'll go back first. You can contact me anytime if you have any other questions."
"Mm." Luo Yan saw him to the door, watching him walk into the twilight at the end of the corridor. The shadow of his hoodie was stretched long by the setting sun, like a gentle tail.
The moment she closed the door, she realized her heart was pounding, and the warmth of the milk glass still lingered on her fingertips. A little over half a glass of milk remained on the table, and the mist on the glass gradually dissipated, revealing a detail she hadn't noticed—a very faint lip print on the rim, clean and neat, like the way he held a tennis racket.
Their contact gradually increased again. It was no longer just cold emails; they would occasionally exchange text messages, all about the project, but with a touch more personal warmth than emails.
Qi Sheng posted: "We collected some interesting data today. A newbie turned the serve into a shot put. Do you want to take a look?" He also included a clumsy emoji of a cartoon bear holding a tennis racket, which Luo Yan recognized as his own drawing.
Luo Yan replied: "Added to the 'Error Case Library', and added a 'shot put serve' tag to the algorithm." This was followed by a smirking emoji.
They still didn't mention the past, but through these small interactions, they slowly rediscovered a familiar rhythm. Just like now, Luo Yan looked at Qi Shengkai's shared folder on the screen, inside which lay a subfolder called "Old Photos." After hesitating for a long time, she finally clicked on it.
It wasn't a photo, but a video, filmed seven years ago at the provincial competition. The footage was a bit shaky, probably shot with a mobile phone, and the camera was focused on a boy in a white tracksuit on the field—it was seventeen-year-old Qi Sheng.
He was thinner than he is now, and his movements were as lithe as a deer's. His wrists rotated as fast as lightning when he hit a backhand shot, and the cheers from the sidelines almost burst through the screen. Luo Yan watched him clench his fist when he won the crucial point and suddenly remembered Su Yu saying with red eyes in the bookstore last year, "He said back then that tennis was his life."
At the end of the video, the camera pans to the stands and focuses on the face of a girl holding a support sign—it's Su Yu. Back then, she wasn't as sharp as she is now, and the light in her eyes was brighter than a spotlight.
Luo Yan turned off the video, her heart feeling as if it were being gently squeezed. She had always thought that Qi Sheng gave up tennis because of Su Yu's departure, but now she realized that it was more like a self-exile—he didn't hate tennis, but hated himself for being distracted on crucial points.
She was startled when her phone vibrated. It was a text message from Qi Sheng: "Are you busy? I have some data I'd like you to take a look at."
"Yes." She replied, took a deep breath, and dragged the "Old Photos" folder into the encrypted area. Some things from the past are not yet ready to be faced with equanimity.
When Qi Sheng arrived, he was holding a tablet computer with a strange set of data on the screen: the same action of the same student was judged as "correct" by the system in the morning test, but as "incorrect" in the afternoon.
"I checked the equipment, it's fine." He placed the tablet on the table. "Could it be a problem with the stability of the algorithm?"
Luo Yan pulled up the environmental parameters for the two tests and suddenly laughed: "Look at the light intensity. In the morning it was sunny with an illuminance of 8000 lux; in the afternoon it was cloudy with an illuminance of 3000 lux. The algorithm's 'reflection point tracking' module is too sensitive to light."
Qi Sheng's eyebrows twitched: "Do we need to add a 'light compensation' algorithm?"
“Hmm,” Luo Yan typed, “but it’s a bit troublesome; we have to retrain the model.”
The sky outside the window darkened, and the lab lights automatically turned on, casting a warm yellow glow on the two of them. Qi Sheng watched her fingers flying across the keyboard and suddenly said, "Let me treat you to dinner as a thank you for helping me revise the algorithm."
Luo Yan's fingers paused: "No need..."
"It's not just polite talk," he interrupted her, his tone serious. "The sweet and sour pork ribs in the cafeteria are on special today. Didn't you always say the cafeteria's ribs were delicious?"
She seemed to have her heartstrings touched, and the surprise in her eyes was impossible to hide.
The sweet and sour pork ribs that day were indeed very sweet, coated in an amber-colored sauce, piled on a white porcelain plate like a small sugar mountain. Luo Yan picked up a piece that wasn't very flavorful, put it in her mouth and chewed it slowly, listening to Qi Sheng tell her things she didn't know.
“That boy who keeps getting the system to make mistakes is actually a sports student. He used to train in weightlifting, and his wrist strength was too great, so he couldn’t control his strength.” He poked at the rice in his bowl with his chopsticks. “I made him soak his hands in warm water every day, and now he’s much better.”
“You seem to know a lot about how to teach beginners,” Luo Yan said.
“The kids I used to coach on the school team,” he said, his voice lowering. “were much harder to teach than today’s college students. It was common for them to cry and say, ‘I’ll never play basketball again.’”
Luo Yan recalled the recording in the "Mistakes" folder where he told the child, "Don't rush, practice slowly," his patience as soft as cotton. She suddenly asked, "Why don't you become a coach?"
Qi Sheng paused, his hand holding the ribs he was picking up paused, and a drop of sauce from the ribs dripped onto the table like a small red dot. He remained silent for a long time before whispering, "I'm afraid I won't teach him well."
It's not that I "don't want to," it's that I'm "afraid."
Luo Yan's heart sank slightly. She seemed to understand a little. He wasn't against tennis; he was afraid of facing that feeling of helplessness again—wanting to do well but messing it up. Just like that match in the provincial tournament, just like last winter in the bookstore when he said, "I'm not worthy of your light."
On the way to the lab after lunch, as they passed the basketball court, a basketball rolled to their feet. Luo Yan bent down to pick it up, but Qi Sheng was a step ahead of her. The moment his fingertips touched the surface of the ball, it suddenly deflated, making a long hissing sound, and became a crumpled piece of rubber.
Both of them were stunned.
"The quality is terrible." Luo Yan laughed first, breaking the awkward silence.
Qi Sheng, clutching the deflated basketball, suddenly said, "Actually... I occasionally go to watch youth games now."
Luo Yan paused in her steps.
"It's at the city stadium, a charity match on the weekend." His voice was very soft, as if he were telling a secret. "Those kids are clumsy at playing ball, but they dare to fight more than I did back then."
He didn't finish his sentence, but Luo Yan understood. In those children, he saw what he had lost—not skills, but the courage to not be afraid of making mistakes.
Back in the lab, the algorithm's "light compensation" module had just finished debugging. The recognition result for the 17th set of data turned green as "correct," and the light spots on the screen gradually softened as the algorithm was optimized, like the surface of a lake being rippled by an evening breeze.
Looking at the screen, Qi Sheng suddenly said, "I'm going to collect motion data from the youth group tomorrow. Do you want to come along?"
Luo Yan looked up at him. The light from the streetlamp shone through the window onto his face, half bright and half dark, as if hiding hesitation and expectation.
"Okay." She heard herself say, her voice as soft as a sigh, yet carrying an unprecedented certainty.
The next day, the city gymnasium was filled with children in brightly colored sportswear. They chased after tennis balls, their laughter louder than the sound of the balls hitting the shuttlecock. A little girl with braids threw the ball in her face while serving, but instead of crying, she put her hands on her hips and shouted, "I'll do it again!"
Luo Yan held up the camera, looked at the scene in the viewfinder, and suddenly laughed.
Qi Sheng stood in the center of the court, wearing a plaid shirt with the sleeves rolled up to his forearms. He patiently taught the child how to hold the racket, and the moment his fingers touched the racket, Luo Yan noticed that his fingertips trembled slightly, as if touching something precious.
"Teacher Qi, why don't you play one too!" the little girl called out, looking up at her.
The surrounding children joined in the commotion, and Qi Sheng's face turned a little red as he waved his hands repeatedly, saying, "It's been a long time since I've played."
"Just one! Just one!"
Luo Yan held up the camera, the lens steadily pointed at him, and suddenly felt a little expectant.
Qi Sheng finally picked up the racket. It was a children's racket, pink, quite disproportionate to his tall stature. His tossing motion was a bit clumsy, and the sound of his hit was very soft. The ball didn't fly over the net and landed in the center of the court, like a perfectly round period.
The children cheered, clapping and shouting, "Go, Teacher Qi!"
Qi Sheng stood there, holding the pink racket, and suddenly smiled. It was a smile Luo Yan had never seen before; the light in his eyes was brighter than a spotlight, like sunlight falling on a lake when the snow first melts.
Luo Yan pressed the pause button, freezing this moment in the camera.
She knew that some things were slowly changing.
Just as algorithms need constant optimization to become more accurate, people's hearts also need repeated testing and getting closer to slowly untangle the knots of the past. Between her and Qi Sheng, there was the regret of the provincial competition, the coldness of last winter, and too many unspoken words. But at this moment, in the laughter and sunshine of the venue, those distances seemed to be slowly shrinking, like errors corrected by data, gradually approaching zero.
On the way back, Qi Sheng put the pink tennis racket in the trunk. Luo Yan looked at his profile and suddenly said, "Next time, let's try using your motion data to train the model."
Qi Sheng paused on the steering wheel. In the rearview mirror, his gaze met hers, and it felt like an electric current ran through him.
“Okay,” he said.
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