residual

Jiang Mo tucked the invitation note into the title page of her textbook, *The Polar Coordinate Principle*. The words "confidence interval" rippled through her heart like a pebble thrown into a deep pool. She didn't reply immediately, nor did she head to the B3 terrace at eight o'clock that evening. An almost instinctive caution kept her in place—in a data stream where the situation was unclear, rashly responding to a sudden anomaly was unwise.

She needs more samples to confirm whether this invitation is a rational output after algorithm iteration or an accidental "noise" in the system's operation.

The atmosphere in the laboratory the following day was subtle. Jiang Mo operated the instruments and recorded data as usual, but her eyes would unconsciously sweep over the focused figure in the control room. Shen Zhiyan also returned to his usual state, rigorous and efficient, discussing a standardized data collection process with Researcher Zhou for nearly twenty minutes. His wording was precise, his logic rigorous, and there was no trace of personal emotion in his voice.

It was as if that note was just a hallucination for her.

Just before her lunch break, Jiang Mo encountered a tricky dimensionality reduction problem while processing a set of high-dimensional data. No matter how she adjusted the parameters, some information was always severely lost after dimensionality reduction, causing a significant drop in the performance of the subsequent classification model. She frowned as she looked at the unsatisfactory results on the screen.

"It is the embedding distortion problem in manifold learning."

Shen Zhiyan's voice rang out from not far away. He had walked over at some point, his gaze falling on the tangled mess of data points on her screen.

Jiang Mo looked up, waiting for his next instructions, which would most likely be filled with technical jargon, or for him to point out her operational mistakes.

However, Shen Zhiyan only took two steps closer, extended his index finger, and pointed to a distinctly colored area on the screen: "Look, the local geometric structure of this part of the data is significantly different from the main distribution. Forcing a uniform linear method to reduce dimensionality is like using a flat map to depict undulating hills; it will inevitably lose altitude information."

His explanation remained professional, but he used concrete metaphors such as "hills" and "maps," which was a rare "dimensionality reduction" explanation for someone who was used to using terms such as "high-dimensional manifold" and "local linear embedding."

"Then... what should we do?" Jiang Mo asked, following his words.

Shen Zhiyan operated his tablet, quickly brought up an algorithm interface, swiped his finger a few times, and then turned the screen towards her: "We can try this spectral method based on locality-sensitive hashing. It allows data to have different 'map scales' in different regions. Although the computational complexity is higher, it can better preserve... the original shape of the 'hills'."

He paused, then added in a calm, factual tone: "The data you collected has strong internal heterogeneity, and a simple linear model is insufficient to capture all its features. This is not an operational error, but a problem with model selection."

This last sentence, spoken casually, extricated her from potential "questioning of her competence." He didn't accuse her of choosing the wrong method, but objectively pointed out the mismatch between the characteristics of the data itself and the model.

Jiang Mo looked at the more complex algorithm flowchart on his tablet screen, a slight thought stirring within her. He had not only pointed out the problem but also provided a better solution, and even... subtly protected her professional dignity.

This is a kind of extremely subtle thoughtfulness hidden beneath rigorous academic guidance.

She began trying the spectral method he suggested. The process was indeed much more complex, with tedious steps and more precise parameter settings. When she reached a crucial step requiring the input of a key parameter, she hesitated. The interface suggested a wide range of values, each potentially leading to drastically different results.

She glanced at Shen Zhiyan instinctively. He was facing away from her, adjusting something on another piece of equipment.

Just as she was hesitating, her personal phone, which was placed next to the control panel, suddenly lit up, and a new WeChat message popped up.

Sender: Data Science Center - Shen Zhiyan

The content contains only a single, isolated number: "0.85".

There is no context, no explanation.

Jiang Mo's heart skipped a beat. She looked up, but Shen Zhiyan still had his back to her, as if the message had nothing to do with him. She looked down again to confirm the number, and then quickly entered "0.85" into the algorithm parameter box.

The model started running, and the progress bar moved smoothly. The final results showed that the dimensionality-reduced data distribution was clear, and the features were fully preserved, achieving unprecedented results.

He actually remembered her private WeChat ID (presumably from the contact information registered by the program team), and used this almost clandestine method to deliver the most crucial parameter when she needed it most.

This precise, roundabout, and emotionless "help" is perfectly in line with Shen Zhiyan's style. Like a top-tier hacker, silently modifying a crucial piece of code in the massive system backend, resolving the user's predicament, yet never revealing their accomplishments.

Jiang Mo looked at the perfect result on the screen, then at the lonely "0.85," and a complex and indescribable emotion welled up in her chest. She suddenly felt that the seemingly indifferent man standing at the pinnacle of data might also possess a certain quality similar to "Lu Gen"—his true nourishment and intentions were buried deep beneath unseen soil.

After the afternoon recording ended, Jiang Mo didn't leave immediately. She waited until almost everyone in the lab had left before slowly packing up her things. Shen Zhiyan was still there; he seemed to be checking the equipment they would be using tomorrow, his movements meticulous.

Jiang Mo paused briefly at the lab door, as if it were just a casual remark; her voice was low, yet clear enough to carry behind her:

"The view from the B3 terrace is indeed quite good."

After saying that, she left without looking back. Her clear footsteps echoed in the corridor, fading into the distance.

She gave him a response, a confirmation that she had received the signal. But the content remained at the level of evaluating the objective environment.

In the laboratory, Shen Zhiyan's movements as he inspected the equipment froze for a fleeting moment after hearing those words. He lowered his head, his bangs obscuring his eyes, and only he could feel that his heart, accustomed to a steady beating, had been injected with a tiny, uncomputed "residual"—an offset that could not be perfectly fitted by the existing model—at that moment.

He needs time to analyze and understand the meaning of this "residual" and the potential disturbance it will cause to the entire system.