In the afternoon, the grove.

After Cheng Nuo finished class, he went to the appointment on time.

On a stone table used to rest in the grove, Wang Genji was already waiting here.

Seeing Cheng Nuo coming, Wang Genji waved his hand at him, "This way, this way." ”

Cheng Nuo came to the stone table and sat opposite Wang Jiji.

The grove is an inaccessible area on campus. Except for the occasional couple who are reluctant to spend money to stay in a hotel, few people come here.

The wind stirs the leaves and makes a rattling sound.

In the quiet grove, on the stone table, Cheng Nuo and Wang Genji sat opposite each other.

"We ...... Let's go. Wang Genji glanced at Cheng Nuo, took off his coat, and spoke slowly.

Cheng Nuo nodded lightly and took a deep breath, "Well, senior, come on!"

Wang Genji took out a stack of A4 papers from the schoolbag beside him.

It was his pre-printed paper. There are seven pages in total.

He handed the printed paper to Cheng Nuo and looked at Cheng Nuo with longing eyes, "Now can you tell me which step of my paper went wrong?"

Yesterday all night, because he had been thinking about it, he didn't sleep well all night.

No, this afternoon, as soon as he finished lunch, he came to this grove and waited for Cheng Nuo early.

Even if it is death, it must be understood.

Wang Genji didn't know if he could salvage this paper. But at the very least, he needs to know where he went wrong.

Cheng Nuo took the paper with a smile and shrugged, "Of course you can." ”

Cheng Nuo took out a pen from his pocket, flipped to the second page of the paper, and drew a heavy horizontal under a formula. "Ah, that's it. Senior, how did you get from the previous formulas to this formula?"

The formula drawn by Cheng Nuo is one of the first few derivation formulas of the new type of solution proposed by Wang Genji.

In the paper, Wang Genji writes that a Black-Scholes random differential equation, e.g., d£=£1 (udt+σdB1)

Write the pseudohomogeneous differential equation of this random differential equation, d£=σ£dB, so ......

Then let an equation f(x)=c(t)e^σB*t be substituted into the pseudohomogeneous differential equation of the original equation after the first derivation, and then use the Riemann integral to solve it, and finally use the Ito formula to find the differentiation.

The key is the process of substituting the maximum value of the first-order derivative of f(x) written by Wang Genji.

"What's the matter, is there anything wrong with this step?" Wang Genji looked confused.

He thought Cheng Nuo would say that the mistake he made was in the middle and late parts of the paper.

After all, there are too many and complicated steps to calculate the formula in the latter part of the paper.

Wang Genji is not 100% sure that he will make a mistake somewhere.

But Cheng Nuo, pointing to the place to show himself, is in the first few formulas of the paper.

Cheng Nuo saw that Wang Jiji's mind hadn't turned around yet, so he frowned slightly, and patiently explained, "Senior, you set a f(x)=c(t)e^σB*t here, and then substitute the maximum and minimum values of its first derivative. ”

"But how can you be sure that the f(x) you set, his first-order reciprocal, must have a maximum value, or a minimum value?"

"+∞ and -∞, both are possible!"

"When the maximum value of the first derivative is positive infinity, or the minimum value is negative infinity, the following formula is simply not true. ”

Cheng Nuo finished his judgment word by word.

Opposite Cheng Nuo, after listening to Cheng Nuo's words, Wang Genji's face had turned pale.

Wrong!

This place, he really was wrong!

When he was writing this piece, he just wrote it off. Or rather, some take it for granted.

There is no consideration at all that there will be a situation where there is no maximum or minimum value.

As a result, a small mistake caused the entire paper to collapse.

Now, after more than four months of hard work, all of them have come to naught.

I'm really unwilling!!

But what can be done then?

There is such a big mistake in the paper, even if it is a major repair, I am afraid that it will not be able to be saved.

No more fun!

Wang Genji smiled bitterly, picked up the paper on the stone table, tore it up violently, and threw it into the air.

Broken pieces of paper were sprinkled one after another.

Wang Genji is like a loveless appearance.

Cheng Nuo looked at Wang Genji with a confused expression, "Senior, what are you doing with the paper?"

Wang Genji was stunned for a moment, and spoke in a very painful tone, "Cheng Nuo, you don't need to comfort me, I've already seen it." ”

"Isn't it just a SCI paper, trivial, really, trivial. ”

"This paper is scrapped anyway, and it's not interesting to be sad. In the future, if I have the opportunity, I will try my best to write a satisfactory SCI paper. ”

After speaking, Wang Genji got up, put on his schoolbag and was about to leave.

The back is bleak and desolate.

Cheng Nuo called Wang Jiji, "Senior, I don't seem to have said it...... This paper can't be revised!"

"What?!" Wang Genji suddenly turned around and looked at Cheng Nuo with a deep shocked gaze, "Cheng Nuo, you ...... What did you just say?"

Cheng Nuo repeated the words with a smile, "Senior, this paper of yours is actually not as bad as you think. Change it, it should still work. ”

"Are you telling the truth?"

"Senior, I don't have to lie to you. In your paper, you proposed a simple solution to the linear random differential equation, and I also calculated it. Theoretically, this method of first finding the pseudohomogeneous equation and then verifying the solution of the variable constant is indeed feasible. However, in the specific calculation process, it needs to be carefully considered. ”

After listening to Cheng Nuo's words, the expression on Wang Genji's face quickly turned from cloudy to clear.

It's good to have a rescue!

He continued to sit opposite Cheng Nuo, looked at Cheng Nuo with cordial eyes, and said with a smile on his face, "Cheng Nuo, come, let's discuss it in depth." ”

Subconsciously, Wang Gengen wanted to take out the printed paper from his school bag. Then I tragically realized that the paper had been torn apart by myself.

There was no way, Wang Genji could only climb under the stone table and try to put the torn paper back together.

At this time, a cleaning aunt passed by. Glancing in the direction of the stone table, his eyes widened.

From her point of view, at the stone table, two boys, one lying under the stone table, kneeling on their knees, their hands on the ground, their heads blocked by the legs of the other boy. What's more, the body of the boy lying under the stone table was still moving back and forth. The other boy leaned back slightly, with a very comfortable expression.

That picture, tsk tsk......

"Are young people so open now?"

The cleaning aunt sighed that she was really old. Is the current social climate so open?

The cleaning aunt kindly reminded the two and shouted loudly. "Hey, two young men, don't do any foreplay, hurry up and do it, I see someone coming towards this place. ”

Cheng Nuo + Wang Genji: "???"