Chapter 492: I met a pervert today

Xu Qingzhou came up with a cross-application problem of ordinary differential equations, partial differential equations, and linear algebra.

The first part first considers second-order linear ordinary differential equations, the second part converts second-order ODEs into first-order linear equation systems, and the third part is a one-dimensional wave equation, which needs to consider the connection with the eigenvalue problem of the matrix in the second part.

Step by step.

Assessing the mastery of differential equation theory, matrix analysis, and PDE solution methods, emphasizing the ability to transfer mathematical tools between different fields.

Of course, there was also a small trap in it, matrix exponential calculation; if one misused the real Jordan form and forcibly separated the imaginary part, it would lead to complex expressions.

Ma Ersi finished reading the problem and instantly widened his eyes: "Professor, is this what you said was not difficult?"

"I think it's within your capabilities."

Xu Qingzhou shrugged.

These problems had considerable difficulty for sophomores, but neither Sun Simin nor Ma Ersi were ordinary people, in Xu Qingzhou's view, they were.

Ma Ersi showed a lifeless expression, his tone resentful: "Professor, not everyone is as powerful as you."

Xu Qingzhou looked at the time and said: "You have 2 hours to get these problems done."

"Mm." Sun Simin nodded heavily, picked up her pen, and started calculating.

Ma Ersi's lifeless expression stiffened, and seeing that Sun Simin had already started, he didn't waste time either, concentrating his attention.

Xu Qingzhou also sat down, took out the data Song Yao gave, and continued to perfect the model. After a while, Carson also checked the equipment operation and came out.

Seeing Sun Simin and Ma Ersi fighting hard, he didn't speak and went back to his seat to sit.

These two little partners were quite interesting, and had some strength; the assessment should be no problem.

Time passed slowly.

There were already several manuscripts in front of Xu Qingzhou, and he was considering how to do the Fourier transform.

"Professor, I'm done."

Sun Simin's voice rang out in the office, pulling Xu Qingzhou back to reality.

11:30.

Half an hour faster than the time Xu Qingzhou stipulated.

To one side, Ma Ersi stared at the problem at hand like a sculpture, seemingly isolated from the outside world, and was not affected.

Xu Qingzhou took the manuscript Sun Simin handed over.

After a long while.

"Mm, not bad."

Xu Qingzhou nodded slightly and said with a smile: "You have already passed."

Sun Simin's small face, which was tense due to nervousness, finally relaxed, patted her chest, and let out a long breath.

At this time, Ma Ersi stood up abruptly, "Professor, I'm done too."

Xu Qingzhou took Ma Ersi's manuscript.

The same problem, but the two people's calculation methods were completely different.

Sun Simin first verified the uniqueness of the equation.

Using the Picard-Lindelöf theorem, the equation coefficients were continuous functions and Lipschitz continuous, proving that the existence and uniqueness of the solution were satisfied, and finally, the solution showed exponentially decaying oscillation.

While Ma Ersi solved it directly with the characteristic equation,

The former deeply applied matrix diagonalization, Sturm-Liouville theory, and Fourier analysis, while the latter solved the problem concisely and efficiently through basic algebraic operations and direct separation of variables.

"Congratulations, you passed too."

After a while, Xu Qingzhou nodded with satisfaction, looked at the two, and said: "Not bad, both avoided the traps I buried in the problem."

Facts proved that his vision was good; the two people in front of him were both talents.

Being able to enter MIT, at the very least, passed the threshold of ordinary people, and next was to compete on talent; these two were not weak either, as long as they finished the three books he arranged.

There was an 80% probability of passing.

Finally, plus 20% carefulness.

"I have a book list here, you can take a look when you have time."

Xu Qingzhou handed over another manuscript, on which were the books he recommended; as long as they were all read, at the very least, they would be invincible at the undergraduate stage.

Xu Qingzhou prepared to go to the library to write the model School Beauty Song gave, stood up, and said: "Carson, leave it to you here."

Boss, well, just arrange the tasks.

He wasn't needed now.

Letting Carson stay in the laboratory, Xu Qingzhou carried his computer to the library; the environment was pleasant, convenient for checking data, and there was nothing for him here for the time being.

However, at the intersection, Xu Qingzhou stopped.

"What the hell?"

Opposite him was the old man he saw in Wilson's office last time.

The expression...

Indescribable, as if he wanted to eat him.

That resentment that made one's back chill was even thicker than last time.

Xu Qingzhou shook his head, subconsciously quickened his pace, took a turn, and that strange gaze disappeared, which made him let out a breath.

"This old pervert wouldn't be targeting me, would he?" Xu Qingzhou felt more and more strange.

"Must be on guard."

He muttered in his heart, but he wasn't very scared; just an old man like that, one punch each, the kind that wouldn't even blink.

Arriving at the library. Xu Qingzhou found a seat by the window and took out his computer.

【Continuous Fourier Transform (CFT): 【f(\omega)=\int_{-\infty}^{\infty}f(t)e^{-i\omegat}dt】】

"Assuming Tesla's stock price is sampled once per second, collecting a total of 60 seconds of data ((n=60)), the goal is to detect whether there is periodic fluctuation to trigger a short-selling signal, then input the 60-second price sequence (x【n】) into the DFT formula..."

Xu Qingzhou thought for a while, stood up, went to the bookshelf, and took out a book "Algorithmic Trading and Market Making Strategies".

The book recommended by Song Yao, which explained in detail the implementation details of strategies such as order book analysis, liquidity hunting, and statistical arbitrage.

At 6 PM, Xu Qingzhou packed up his things and went back to the laboratory first, let Carson and the others get off work first, he himself stayed until 8 o'clock, finally checked the instrument again, closed the door, and went home.

Song Yao sat cross-legged on the sofa, looking at the computer screen, considering how to perfect the algorithm model. When thinking, she would reveal a cold aura that kept strangers away.

"I'm back."

Xu Qingzhou walked over to see what Song Yao was struggling with.

Hidden Markov Model.

School Beauty Song turned her body slightly, hugged Xu Qingzhou's waist, looked up, the coldness just now disappeared, replaced by a pitiful expression, "Professor Xu, so tired."

"Want to try Xu-style massage?"

Xu Qingzhou helped her tidy up the little broken hair on her forehead, a small one, inexplicably feeling very cute.

"Hug me." Song Yao shook her head.

Xu Qingzhou nodded, sat down, and hugged School Beauty Song's waist. Coming back after a tiring day and curling up on the sofa with the person he liked was extremely comfortable.

Er Miao circled in front of the two, found there was no place for it, could only meow resentfully, and went to the windowsill to lie down.

Outside the window, the twilight was a bit thick, and the bright lights of the city in the distance could be vaguely seen.

Xu Qingzhou let out a long breath, his thoughts gradually drifting away. This month, get School Beauty Song's model out, and in terms of experiments, at the very least, it must enter the stage of industrial iteration.

What is process iteration? The precursor has been verified, only need to constantly change parameters to improve sample performance. They currently... don't even have a complete sample.

Xu Qingzhou remembered the old man he met at the intersection this afternoon again.

Song Yao buried her head in Xu Qingzhou's arms, seeing him not speaking, seemingly in a daze, couldn't help but ask: "What are you thinking about?"

"About the pervert."

Song Yao's Qilin arm was about to be raised again.

"I mean, I met a pervert today."

(End of chapter) ===== CHAPTER 493 =====