My IQ has been increasing year by year.

Chen Zhuo walked under the gourd tree, carrying a kettle filled with cooled boiled water.

Push open the heavy doors of the old library.

Behind the lending section in the lobby on the first floor, the librarian, wearing reading glasses, was dozing off in a wicker chair, with a faint Huangmei opera playing on a radio next to him. Chen Zhuo tiptoed up the stairs to the third floor.

At the end of the corridor is the foreign language periodical reading room.

Chen Zhuo pushed open the door and went in. Several ceiling fans were spinning slowly on the ceiling.

The huge reading room was completely empty; there wasn't a soul in sight.

someone.

At the end of a row of bookshelves, the sound of metal rollers scraping against the ground could be heard.

Chen Zhuo followed the sound.

A short-haired girl was bending over, unloading heavy periodicals from a trolley full of old foreign language books and sorting them into categories as they were placed on the bookshelf. Su Wei.

Chen Zhuo didn't make a sound to disturb her, but simply stood at the other end of the bookshelf and quietly watched her work.

Su Wei worked very efficiently, even with a mechanical precision.

She picked up a book, glanced at the call number on the cover, and without even pausing, turned around and precisely slipped it into the corresponding slot. Clean and efficient.

The number of books on the cart gradually decreased.

Su Wei straightened up, let out a long breath, wiped the sweat from her forehead with the back of her hand, and turned to walk towards a large desk by the window in the reading room. That was her stronghold.

On the corner of the table sat a surprisingly large plastic water bottle, next to a tall stack of draft paper and a brick-thick book, "Probability Theory and Mathematical Statistics." The pages were worn and curled, covered with dense annotations in red and blue ballpoint pens.

She sat down, unscrewed the kettle, took a big gulp of water, and immediately picked up her pen, burying herself in the long string of complex formulas on the draft paper. Chen Zhuo took a few steps closer and stopped two tables away from her.

"What a coincidence."

Su Wei paused, her pen still, and looked up.

Upon recognizing Chen Zhuo, her expression remained largely unchanged; she merely raised an eyebrow slightly and put down her pen. "Borrowing a book?"

Her voice was clear and crisp, with a slightly hoarse quality.

"Um."

Chen Zhuo nodded and walked to her desk.

"Find a few review articles on discrete topology and graph theory from the 1960s and 70s. You don't need specific papers, just bound volumes of several mainstream mathematics journals from that era." Su Wei didn't say anything.

She didn't even glance at the sluggish 586 computer behind the borrowing room; that kind of ancient system took two minutes just to wait for the cursor to blink before making a search. She simply sat there, her eyes slightly closed.

Less than three seconds.

"Area C"

Su Wei opened her eyes, her tone as calm as if she were recalling something in her own home.

"The third row of bookshelves, the sixth cabinet from the left, the bottom shelf, about the third or fourth stack on the right."

"besides."

Su Wei added a sentence.

"Those books are positioned right opposite the west-facing window, where the afternoon sun shines very intensely. The green covers are probably already faded or discolored from the sun. When you're looking for them, don't just focus on the color; look at the call number. The prefix is ​​011."

Chen Zhuo looked at her and suddenly smiled.

"You're even including color fading from sun exposure?"

Su Wei picked up her pen again and looked down at her draft paper.

"It's common sense. Books in that area, especially those with dark covers, will generally change color after three years. Go get them while it's still light; the bottom floor isn't well-lit." Chen Zhuo didn't say anything more and turned to walk towards Section C.

Following the coordinates provided by Su Wei, he crouched down and searched through the pile of old books on the bottom shelf.

Sure enough, on the third stack on the right, he pulled out several thick periodicals with covers that had turned white from the sun and edges that were frayed. Chen Zhuo took the books and returned to the table by the window.

He didn't sit opposite Su Wei, but instead sat two seats away in a well-lit spot.

I took out a few blank A4 sheets of paper and a pen from my bag and laid them flat on the table.

I opened that Russian journal, which smelled of musty books.

The entire text is interwoven with Cyrillic letters and complex mathematical symbols, resembling a long-abandoned labyrinth.

Chen Zhuo's eyes quickly scanned the pages of the book, his mind automatically filtering and translating.

He observed and learned how mathematicians in history constructed logic.

The pen tip landed on the paper, making a soft scratching sound.

The reading room returned to silence.

Only the ceiling fan overhead was spinning, and occasionally a clear bird song or two drifted in from outside the window.

The two of them each occupied one end of the long table, and neither of them spoke again.

They were like two fish hunting for food in the same sea, each in their own space, yet they did not interfere with each other.

Time passes little by little.

The shadows cast by the sun slowly lengthened on the floor.

Chen Zhuo put down his pen and stretched his stiff neck.

He is trying to redefine these ancient geometric propositions from an algebraic perspective.

He picked up the kettle, took a sip of water, and glanced at the other end of the long table out of the corner of his eye.

Su Wei was in an almost stiff position, staring intently at the draft paper in front of her.

Her brows were furrowed, and the pen in her hand twirled rapidly between her fingers. Occasionally, she would impatiently cross out a long formula on the paper, then write down an even longer one. Chen Zhuo put down the kettle, stood up, and walked over.

He didn't deliberately lighten his pace, and stopped at a position diagonally opposite Su Wei.

Su Wei noticed the movement, looked up, and her eyes still held an unpredictable anxiety and a hint of displeasure at being interrupted.

"At this rate, it's like you're grinding grain at a snail's pace."

Chen Zhuo spoke gently and made a casual joke.

Su Wei ignored his lame joke, simply pushing the thick "Probability Theory and Mathematical Statistics" book forward, and said somewhat defiantly, "That's how it's written in the book. In financial market risk forecasting, the time variable is continuous. Without using calculus to calculate the expected value, how can you get accurate data?" Chen Zhuo glanced at the dense integral symbols and limit calculations on her draft paper.

This is a typical stochastic process problem used to assess the future trend of a certain financial derivative.

Su Wei clearly wanted to solve the problem strictly according to the textbook's continuous-time Brownian motion model, but the complex calculations were obviously beyond the limits of manual calculation, leaving her in a dead end. "I have a strong desire to make a lot of money, but the tools I chose are a bit clumsy."

Chen Zhuo pulled out a chair and sat down opposite her quite naturally.

"What do you mean?"

Su Wei glanced at him warily.

Chen Zhuo didn't explain, but simply reached out and pointed to the lengthy integral formula on her draft paper.

"Your premise is wrong. In the real financial market, transaction numbers do change over time, but that doesn't mean you have to treat it as an absolutely smooth curve." Chen Zhuo picked up a spare pencil from the table and dragged the paper in front of him.

"If you insist on following this continuous line, you will be overwhelmed by endless tiny fluctuations. Calculating this by hand? That's a computer's job. Although it might be okay for you, it's a waste of your brain to use it here."

He deftly drew several circles in the blank space of the paper, and then connected them with straight lines with arrows.

"Let's look at it from a different perspective."

Chen Zhuo's voice was steady and clear, as if he were stating an extremely common sense fact.

Don't look at the lines, look at the points.

"Break down the continuous timeline and assume that the market only exists in a few key states: it went up today, it went down tomorrow, or it remained flat. Each state transition is only related to the previous state and has nothing to do with anything before that."

Chen Zhuo wrote down several simple probability values ​​next to the circle, then enclosed them in square brackets, forming a square matrix. "Discretize it, turn it into a transition probability matrix, and then you only need to calculate the nth power of this matrix."

He put down the pencil and pushed the draft paper back in front of Su Wei.

"Markov chain?"

Su Wei looked at the extremely clean square formation on the paper, and her eyes lit up slightly.

"right."

Chen Zhuo leaned back in his chair.

"By reducing a complex continuous problem to a discrete algebraic problem, the computational load is reduced by at least half, and the error tolerance is much higher than your calculus, which is precise to several decimal places." Su Wei didn't speak. She picked up her pen and tried to fit the data from the previous problem into the matrix that Chen Zhuo had drawn.

A few minutes later.

The previously intractable computational bottleneck was suddenly cut open as if by a sharp dagger.

The complex integration process is perfectly replaced by matrix multiplication, and the final expected value is clearly stated on the paper.

Su Wei put down her pen, looked at the result, and let out a long sigh.

She looked up, her gaze somewhat complicated as she looked at Chen Zhuo sitting opposite her.

"How do you know so much about the underlying logic of financial actuarial science?"

Chen Zhuo smiled.

"I don't understand finance, but I do understand math and I'm good at shirking my responsibilities when given the opportunity."

He pointed to the bright sun outside.

"In this sweltering heat, brain cells are a non-renewable resource. Using the most cumbersome methods to calculate them can easily lead to heatstroke. Those formulas are ultimately just tools. If a hammer doesn't work, why not try a wrench?"

Su Wei looked at him, and for the first time ever, the corners of her mouth twitched slightly, revealing a very faint smile.

Thanks.

The thank you was a bit stiff, but it was very sincere.

"You're welcome."

Chen Zhuo stood up and pointed to the bookshelf in the distance.

"Now that we're even, could you do me another favor? Do you have a bound volume of the 1975 issue of the Bulletin of the American Mathematical Society?"

Su Wei didn't hesitate at all.

"Section F, first row, top floor. You might need to bring a small stool, as those books are quite thick and placed very high."

"it is good."

Chen Zhuo turned and walked towards Sector F.

Su Wei watched his retreating figure, then glanced down at the simple yet powerful matrix on the draft paper.

This is a more efficient, but also more ruthless path.

Chen Zhuo carried the thick "Bulletin of the American Mathematical Society" back and sat down in his seat again.

As darkness fell outside, the glow of the setting sun streamed through the windowpanes, casting long, orange-red streaks across the floor. Inside the reading room, only the sounds of the fan whirring and the turning of pages remained.

Chen Zhuo wrote down the eigenvalues ​​of the last row of the matrix on the draft paper.

He put down his pen, neatly folded the pages filled with formulas, and tucked them into his notebook.

After packing his things, Chen Zhuo picked up his water bottle and prepared to leave.

As I passed by Su Wei's table, she was still frantically performing matrix operations with her head down.

Chen Zhuo casually greeted him.

"Um."

Su Wei did not look up.

"Will you come again tomorrow?"

"Come on, there's still a lot to see."

"Okay, if you need to find something tomorrow, write down the era and general category on a note for me in advance."

Su Wei spoke calmly, as if she were arranging a work coordination.

"it is good."

Chen Zhuo pushed open the wooden door of the reading room and stepped into the summer evening breeze.