my scientific age

Chapter 96 Xu Xue!

The world of mathematics is really interesting, and Yu Hua learned with great interest. After learning the story of calculus, he completely understood the definition of modern limit.

Limits, perfected and redefined successively by 'the founder of calculus' Cauchy and 'the father of modern analysis' Weierstrass, are the basis of calculus.

Cauchy limit definition - when a variable's successive values ​​approach a fixed value indefinitely, if the difference between it and this fixed value can be arbitrarily small, then this fixed value is called its limit .

Cauchy's definition of the limit is interesting, and although there are factors such as geometry, motion, and intuitive understanding, it circumvents the fatal flaw of Leibniz's infinitesimals.

It can be as small as you want, which means that as small as you make me, I will be as small as I am. I will not go to you. As long as you say a number, I will immediately become this number. If you make me infinitely small, then Say how much the infinitesimal is, anyway, there is always a value that is the limit.

In the hands of Weierstrass, the father of modern analysis, the limit definition of this text is completely described in mathematical language - if and only if for any ε, there exists a δ>0, such that as long as 0< |xa|<δ, there is |f(x)-L|<ε, then the limit of f(x) at point a is L.

The limit mathematical symbol is denoted lim.

"Limits are unique and bounded..." Hua Luogeng saw that Yu Hua sounded without pressure, and the speed of his lectures was getting faster and faster. He quickly passed the definition and properties of limits, and then carefully described the limits of functions.

Function Limit is a foreign course for first-year students of Cambridge University, including infinitesimal and infinity, limit of function and limit of sequence, limit algorithm and two important limits and so on.

Yu Hua silently absorbed the content of Hua Luogeng's explanation. All kinds of obscure mathematical knowledge in his mind were gradually integrated and completely transformed into his own things. I have to say that teaching by famous teachers and self-study are completely two concepts. The former's learning and absorption efficiency is The latter is several times as many.

Time passed slowly, about two hours later.

"Okay, today's class is here for the time being. After I go back, I will write an article about Cauchy's inequality as homework. Is there any problem?" Hua Luogeng looked at the time, chose to end today's class, turned to Yu Hua, and arranged road.

Is this writing an article?

Yu Hua was slightly stunned. The article in Hua Luogeng's mouth was not a copy of a question, but an article about understanding Cauchy's inequality. It was similar in nature to a thesis, and such a 'homework' was assigned in the first class, which was really unexpected.

The two-hour course has gone from the limit to the introduction of calculus. Yu Hua's learning speed is fast, and Hua Luogeng's lectures are naturally fast.

"Okay, no problem." Yu Hua nodded, stood up and bowed to Hua Luogeng to salute: "Thank you Professor."

Cauchy's inequality is one of the contents of calculus, which is easy to understand and not difficult.

Glancing at Yu Hua, Hua Luogeng smiled slightly: "Be careful on the way back."

"Students understand." Yu Hua nodded.

……

The sun is shining brightly, and the thick snow in Tsinghua Garden reflects the light.

There is a new schoolbag on his body, which contains four important English-origin advanced mathematics textbooks. The schoolbag is a gift from his wife, Wu Xiaoyuan, and the style is novel. Yu Hua left Room No. 28 in the West Courtyard and walked out along the aisle. With some time left, he was going to do something to settle the final payment and the title collection of Huangchenggen Bookstore.

The west courtyard is basically a single-family courtyard surrounded by snow. When Yu Hua walked halfway to the west courtyard buildings, suddenly, the door marked NO.11 on the right opened.

"Squeak!" A slight friction sound came out.

Immediately afterwards, a teenager in a student uniform came out, his face was reddish and he looked sick.

"Ah embarrassing!" The next second, the teenager couldn't help but sneezed.

Looking at the handsome boy, Yu Hua smiled and nodded.

The teenager was startled for a moment. It was the first time he saw a strange young man in the Western courtyard at this time, and when he saw Yu Hua's smile, he smiled subconsciously.

Yu Hua continued to smile as he headed towards the entrance of the West Courtyard.

"Zhen Ning, is there any problem?" At this moment, a middle-aged woman in winter clothes walked out, came to the boy's side, and asked with concern.

"It's okay, the medicine is much better, mother, who is that young man?" Young Yang Zhenning shook his head gently. Yesterday, he had a cold and fever at school, and was immediately sent back to Tsinghua Garden by Mr. Ren, and took two pairs of traditional Chinese medicine. Today Feeling much more comfortable, Yang Zhenning said to his mother Luo Menghua as he stared at Yu Hua who was walking away.

Luo Menghua glanced at Yu Hua's back, very unfamiliar, and shook his head gently: "I don't know, maybe it's a student in the school. Do you want to take a rest, sir, I asked you for two days off."

"No, Zhenning is much better now, her studies are very important, and I won't be able to delay for a moment. Jiaxian is still waiting for me at school."

Young Yang Zhenning shook his head again and again. He couldn't stand the life of staying at home. He was about to go to the second year of high school, and his studies were quite tight: "Goodbye mother, you can go back, don't catch a cold."

"Well, be sure to pay attention to safety on the road." Hearing the concern from his son, Luo Menghua smiled softly, his eyes full of love.

"It's from Zhenning Province." The boy smiled.

……

Yu Hua walked out of the quiet and peaceful Tsinghua Garden, called a rickshaw, went straight to Jinguo Hutong in Ping'anli, and went home first. Xu Rui and Xu Erya were very excited to see Yu Hua returning home again, and Tang Yuanyuan also ran away quickly. Come out and stick to Yu Hua.

"Xu Rui, how is the situation at home?" Yu Hua hugged Tang Yuanyuan and went to the main room.

"Sir, everything is business as usual at home. Xu Rui, according to your arrangement, lives in a secluded place and doesn't get involved in external affairs. There have been many shootings during this time, and I heard that it was done by Japanese secret agents." Xu Rui respectfully said.

Yu Hua was thoughtful, nodded, and asked, "Where is Yuanyuan's mother buried?"

"Yiyuan in the western suburbs, No. 682." Xu Rui truthfully gave the location of Yuanyuan's mother's tomb.

"Remember, when Yuanyuan grows up, she will be buried again. Come." Yu Hua came to the front of the main room. After making arrangements, he put down Tang Yuanyuan in his arms and motioned for Xu Erya to watch over him.

After he finished speaking, he turned around and walked into the main room.

The black and white portrait of Yu Qinghe was placed on the table in the main room. The three incense sticks were slowly burning. Yu Hua stepped forward and knelt down, bowed and kowtowed three times.

After the memorial ceremony, Yu Hua took out three more incense sticks and lit them and put them in the incense burner. The surface of the table was clean, and there were no sundries around the main room. Xu Rui and Xu Erya were very attentive to the cleaning of the main room.

"Xu Rui, Erya, how have you been studying during this time?" Yu Hua withdrew from the main room after serving the incense, holding Tang Yuanyuan, who was as cute as a porcelain doll in his right hand, and asked Xu Rui and Xu Erya. .

Upon hearing this, Xu Erya immediately lowered her head, a little embarrassed.

"Sir, Xu Rui is good at learning and can read and write. Erya has never attended a private school and lacks the foundation. She is still literate now." Xu Rui answered truthfully.

"It's good to be able to read. As long as you have the will, you won't be afraid of failing in your studies. If the progress is slow, you won't be afraid of anything. Come on." Yu Hua glanced at Xu Erya, who bowed her head and blushed, smiled and comforted.

"Sir, Erya wants to ask you to name me." Xu Erya looked up at Yu Hua, as if she had made a major decision, gritted her teeth, and said.

Yu Hua was stunned for a moment: "Name? I don't know."

He doesn't know how to name an operation that involves his entire life.

In later generations, many people in China did not value the name, and thought it was just a code name. However, in this era, the name is extremely valued and particular, and no one has any cultural level to dare to take a name.

Yu Hua has a certain level of education, but the problem is... he is a standard-named person.

Otherwise, he would not have remained silent when the lighting source was named.

If you don't understand, don't get involved.

This is Yu Hua's code of conduct.

"Sir, Erya is not afraid, you can choose whatever you want, Erya doesn't want to keep using this nickname." Xu Erya bit her lip and responded.

As soon as these words came out, the courtyard was quiet.

Xu Rui remained silent and did not speak.

"Brother, what is a name?" Tang Yuanyuan asked curiously, revealing her big innocent eyes.

"Just take a name, such as Yuanyuan." Yu Hua stroked Tang Yuanyuan's smooth hair and smiled.

Tang Yuanyuan seemed to understand but didn't understand: "Oh? Is that the sister Erya's name is Xu Yuanyuan?"

"Sister Erya is not called Xu Yuanyuan, your name is Yuanyuan."

Yu Hua laughed and shook his head, his eyes turned to Xu Erya who was in front of him, feeling Xu Erya's attitude and expression, he sighed, thought for a while, and said softly, "I met your brother and sister in winter, just when the snow was over, so I'll be alone. How about a name with snow?"

Xu Xue.

I didn't take any names like Xu Ruoxi, Xu Xuan, etc., just a name that fits the characteristics of a girl.

"Mr. Xie named her, and Erya will be called Xu Xue from now on." Xu Rui thanked him immediately.

"Mr. Erya Xie took the name." Xu Erya, no, now called Xu Xue, with a hint of excitement on her face, saluted and thanked.

"No, Xu Rui, I have something to tell you, wait for you to go to the Huangchenggen Bookstore in the north of the city and ask them to send the printed title collection to the door of Xuanji Zhai. The number is 500. I have already paid the deposit. The final payment is 105 yuan."

Yu Hua shook his head lightly, motioned the two to get up, turned his eyes to Xu Rui, and explained carefully: "After delivery, you will bring all the problem sets home. Every morning at 7:20, you will send 50 problem sets to No. [-] Middle School. Understand?"

"Xu Rui understands."

The smart and clever Xu Rui immediately wrote down what Yu Hua explained.

"This matter is very important, you must remember that this is 105 yuan, give it." Yu Hua instructed, then took out a hundred pen and paper from his body and handed it to Xu Rui.

(End of this chapter)