The meaning of the price difference between purchase and sales of goods or some specific explanations and examples Is there any specific example of the price difference between purchase and sales of goods~ Please attach the definition of "price difference between purchase and sale of goods"

The meaning of the price difference between purchase and sales of goods or some specific explanations and examples Is there any specific example of the price difference between purchase and sales of goods~ Please attach the definition of "price difference between purchase and sale of goods"

The sales price amount accounting method is an inventory accounting method widely used by commodity retail enterprises in China's accounting practice. This method is processed through the "commodity purchase and sales difference" account. Usually, the purchase, sales and inventory of commodities are recorded according to the sales price, and the difference between the sales price and the purchase price is recorded into the "commodity purchase and sales difference" account. At the end of the period

Explain the meaning of swallowing dates with specific life examples About 30 words

Zhang Dawang was not able to do a math thinking problem, so he asked the teacher. After asking, the teacher asked if he knew a little. He said, "I see."

Why is the profit maximum when the marginal income is equal to the marginal cost?

- marginal analysis
The long-distance bus from Hangzhou to Nanjing is about to start. No matter which company's car, the fare is 50 yuan. A hurried passenger saw that there is still a vacant seat in the car of a state-owned company and asked to get on the bus for 30 yuan, but was rejected. He found a car of a private company with vacant seats. Without saying a word, the conductor charged 30 yuan and allowed him to get on the bus. Which company's behavior is more rational? At first glance, the private company allowed the passenger to enjoy the transportation service of 50 yuan for 30 yuan, of course. But if we use the marginal analysis method, the private company is indeed smarter than the state-owned company
Speaking of the word "marginal", many people think it is a little mysterious. In fact, you know that you often unconsciously use this concept to analyze problems
The word "marginal" can be understood as the meaning of "increased", and "marginal quantity" means "increment". To be exact, the independent variable increases by one unit, and the amount increased by the dependent variable is the marginal quantity. For example, the factor of production (independent variable) increases by one unit, and the output (dependent variable) increases by two units, The two units that the dependent variable increases are the marginal output. Or more specifically, the transportation company has added some cars, which can transport more than 200 passengers every day. These 200 passengers are the marginal quantity. The marginal analysis method is to analyze how much the dependent variable will change if the independent variable changes by one unit
We can use the example of the fare of the last passenger to illustrate the usefulness of the marginal analysis method. When we consider whether to let the passenger get on the bus at the fare of 30 yuan, we should actually consider the two concepts of marginal cost and marginal income. Marginal cost is the income (dependent variable) increased by adding a passenger (independent variable). In our example, To add this passenger, there is no need to increase the wear and tear of the car, gasoline cost, staff salary and tolls. For the car, it is the same to pull more and less people. The increased cost is only the food and drinks given to the passenger. Assuming that these things are worth 10 yuan, the marginal cost is 10 yuan. The marginal income is the income increased by adding a passenger (independent variable) (dependent variable). In this example, adding this passenger increases the income by 30 yuan, and the marginal income is 30 yuan
When making a decision according to the marginal analysis method, it is necessary to compare the marginal cost and marginal income. If the marginal income is greater than the marginal cost, that is, the increased income of adding this passenger is greater than the increased cost, it is appropriate to let this passenger get on the bus, which is a rational decision. If the marginal income is less than the marginal cost, it will be a loss to let this passenger get on the bus, which is an irrational decision. From the theory In fact, passengers can be increased until the marginal income is equal to the marginal cost. In our example, it is rational for a private company to let the passenger get on the bus. No matter whether the conductor knows the concept of marginal and marginal analysis, he actually makes a decision according to the principle that the marginal income is greater than the marginal cost. The conductor of a state-owned company does not let the passenger get on the bus, or is strictly restricted We often say that the operating mechanism of state-owned enterprises is not as flexible as that of private enterprises
Marginal analysis is widely used in economics. Therefore, the concept of marginal and the proposal of marginal analysis are regarded as a revolution of economic methods. In economics, the proposal of marginal analysis not only provides a useful tool for us to make decisions, but also enables economics to use mathematical tools. The relationship between the changes between independent variables and dependent variables represented by marginal analysis The system can be expressed by differential. Therefore, mathematical methods can be widely used in economics. Now mathematics is widely used in economics and plays an important role in promoting the development of economics itself and solving practical economic problems. Interested readers will realize this when they look at more advanced economic works

Nash equilibrium, how to understand Please give specific examples,

Nash equilibrium, also known as non cooperative game equilibrium, is an important concept in game theory, named after John Nash
If no participant can act alone to increase revenue in a certain situation, this strategy combination is called Nash equilibrium
The classic example is the prisoner's dilemma, which is a non-zero sum game. The main idea is: two suspects in a case are tried separately, and the police officer tells the two prisoners respectively that if you confess and the other party does not confess, you will be released immediately and the other party will be sentenced to ten years; If both confess, they will be sentenced to two years. If both do not confess, they will be in the best position and will only be sentenced to half a year. Therefore, they fall into the dilemma of confessing or not confessing at the same time. However, they can not communicate, so they both choose to confess according to their own reasons from the perspective of their respective interests. This situation is called Na's equilibrium point. At this time, The individual's rational interest choice is inconsistent with the overall rational interest choice
Academic controversy and criticism
First, the academic proof of Nash's equilibrium fixed point solution on non cooperative game theory is non constructive, that is, Nash proved the existence of equilibrium fixed point solution by Kakutani fixed point theorem, However, we can't point out how to construct the algorithm to achieve the equilibrium fixed point solution. This non constructive discovery has limited effect on the game in real life. Even if we know that the equilibrium fixed point solution exists, we can't find it in many cases, so we still can't solve the problem. [source request] in the mathematical sense, Nash doesn't surpass the fixed point theorem of kiyov
After the intervention of mainstream media such as Sylvia Nasar (book author) and Ron Howard (film author) in the beautiful mind, Kakutani was completely ignored in these people's works. Some people believe that the more appropriate name of "Nash equilibrium" should be called "Kakutani Nash game theory fixed point" (Kakutani Nash game theoretical fixed point) or "Kakutani Nash equilibrium", without Kakutani Nash fixed point theorem, Nash's proof has little academic significance. The way in which Kakutani Nash's key contribution is completely ignored in beautiful mind remains to be discussed
Second, Nash's non cooperative game theory model only breaks through a limitation in game theory. A greater limitation is that game theory often faces complex social and economic behaviors composed of billions of nodes, but von Neumann and Nash's research is a small-scale game theory with two or three nodes (some call it tiny scale toy case). [source request]
The imperfections of this assumption may be better than the assumption that everyone is cooperative More serious. Because in economics, it is extremely impossible for all people in a large society to be cooperative. Non cooperative situations are usually more common in the case of large objects, but have less impact in the small-scale economy with two or three nodes. Since the cooperative premise is changed to non cooperative premise, it still stays in the small-scale game theory with two or three nodes, which can not be ignored Recently, Deng Xiaotie and Yao Qizhi, scholars from City University of Hong Kong and Tsinghua University in Beijing, have made progress in large-scale game theory based on complexity theory
Doctoral thesis of a doctoral student in computer science at MIT (PDF) http://people.csail.mit.edu/costis/thesis.pdf ) ——Constantinos Daskalakis, who is currently an assistant professor in the Department of electrical engineering and computer science at MIT, cooperated with Christos papadimitriou of UC Berkeley and Paul Goldberg of the University of Liverpool in the UK to prove that some games are effective He said that the power of all computers in the world can not calculate the Nash equilibrium point within the whole life span of the universe. Daskalakis believes that computers can not find it and humans can not find it. Nash equilibrium belongs to NP problem. Daskalakis proved that it belongs to a subset of NP problem, which is not generally considered as NP complete problem, but ppad complete problem. This research result is recognized by some computer scientists This is the biggest progress in the field of game theory in the past decade
However, in the same paper, Daskalakis also pointed out that when the participants are anonymous, it only takes polynomial time to approximate the Nash equilibrium
Realistic examples
The above examples may seem unnatural, but in reality, both human society and nature can find examples similar to prisoner's Dilemma and divide the results into the same payment matrix. Economics, politics and sociology in Social Sciences, animal dynamics and evolutionary biology in natural sciences can use prisoner's Dilemma Analysis to simulate the endless prisoner's dilemma faced by organisms Environmental game. Prisoner's dilemma can be widely used to illustrate the importance of this game. The following are examples from all walks of life:
[editor] political science example: arms race
In politics, the arms race between the two countries can be described as a prisoner's dilemma. Both countries can claim to have two options: increasing arms (betrayal) or reaching an arms reduction agreement (cooperation). Neither country is sure that the other will abide by the agreement, so the two countries will eventually tend to increase arms. It seems paradoxical that although increasing arms will be the "rationality" of the two countries Behavior, but the result appears "irrational" (for example, it will cause damage to the economy). This can be regarded as the inference of containment theory, that is, to curb the other party's attack with strong military force in order to achieve peace
[editor] economic example: tariff war
Two countries have two options in terms of tariffs:
Raise tariffs to protect your goods. (betrayal)
Reach a tariff agreement with the other party to reduce tariffs to facilitate the circulation of their respective commodities. (cooperation)
When one country raises tariffs (betrayal) alone due to non-compliance with the tariff agreement due to some factors, the other country will respond similarly (betrayal), which will trigger a tariff war. The goods of the two countries lose each other's market and cause damage to their own economy (the result of common betrayal). Then the two countries reach a tariff agreement again (the result of repeated game is that we will find that the benefits of joint cooperation are the greatest.)
[editor] business example: advertising war
There are also various examples of prisoner's dilemma in commercial activities. Take advertising competition as an example
The two companies compete with each other, and the advertisements of the two companies influence each other, that is, if the advertisements of one company are more accepted by customers, it will seize part of the income of the other party. However, if the two companies issue advertisements of similar quality in the same period, the income will increase little, but the cost will increase. However, if the advertising quality is not improved, the business will be taken away by the other party
The two companies have two options:
Reach an agreement with each other to reduce advertising expenses. (cooperation)
Increase advertising expenses, try to improve the quality of advertising and overwhelm each other. (betrayal)
If the two companies do not trust each other and cannot cooperate, and betrayal becomes a dominant strategy, the two companies will fall into an advertising war, and the increase of advertising cost will damage the income of the two companies, which is a prisoner's dilemma. In reality, it is difficult for the two competing companies to reach a cooperation agreement, and most of them will fall into a prisoner's dilemma
[editor] bicycle race example
The competition strategy of cycling events is also a kind of game, and its results can be explained by the research results of prisoner's dilemma. For example, in the tour de France held every year, there are the following situations: players often travel in large teams before reaching the end (English: peloton) The way forward, they adopt this strategy is to make themselves not too backward and make moderate efforts. The player in the front is the most laborious when facing the wind, so choosing to be in the front is the worst strategy. Usually, this happens, and everyone is unwilling to move forward at first (common betrayal) This makes the speed of the whole team very slow, and then usually two or more players will ride to the front, and then exchange the front position with each other for a period of time to share the resistance of the wind (cooperate together), so as to improve the speed of the whole team. At this time, if one of the people in front tries to keep the front position (betray), the other players and the team will catch up (betray together) Usually, the player with the most times in front (cooperation) is usually caught up (betrayed) by the backward player in the end, because the latter player rides in the rush of the front player, which is relatively effortless
[editor] events related to the prisoner's dilemma
[editor] fantasy
In his book, William Poundstone illustrates the prisoner's dilemma with an example from New Zealand. In New Zealand, newspaper kiosks are neither managed nor locked. People who buy newspapers put down their money and take them away. Of course, some people may take newspapers without paying for them (betrayal), but it is recognized that if everyone steals newspapers (common betrayal) It will cause inconvenient and harmful results in the future, which rarely happens. The special feature of this example is that new Zealanders can get out of the prisoner's dilemma without being affected by any other factors. No one pays special attention to the newspaper booth. People abide by the rules to avoid the consequences of common betrayal. This common reasoning or idea to avoid the prisoner's dilemma is called "fantasy" （magical thinking）”.[3]
[editor] "confession and commutation" is not feasible
The conclusion of prisoner's dilemma is one of the reasons why plea bargain is prohibited in many countries. The conclusion of prisoner's dilemma is that if there are two criminals, one of them commits a crime and the other is innocent, the offender will confess everything and even wronged the innocent (betrayal alone) for commutation The worst-case scenario is that if both of them are sentenced to prison, the criminals who confess will have fewer sentences and the wrongdoers who insist on innocence will have more
[editor] utility tragedy
In reality, there are more than one player in the game, and there will be multiple participants in the prisoner's dilemma. Garrett James Hardin's public goods tragedy is an example: "public goods tragedy refers to that all public property belonging to the most people is often the least cared for." For example, in fisheries, fish on the high seas belong to the public. Under the idea that they do not fish indiscriminately and others do not catch indiscriminately, fishermen will fish indiscriminately, resulting in the destruction of marine ecology and the impact on fishermen's livelihood (the result of common betrayal) However, the formulation of multiparty prisoner's dilemma remains to be discussed, because it can always be divided into a group of classical biparty prisoner's dilemma. That is, there are only two-party prisoner's dilemma, and there is no multiparty. The so-called multiparty prisoner's dilemma is just an illusion formed by the mixing of multiple biparty prisoner's dilemmas
[editor] repeated prisoner's dilemma
In his book cooperative evolution, Robert Axelrod explored an extension of the classic prisoner's Dilemma and called it "repeated prisoner's dilemma" (IPD) In this game, participants must repeatedly choose their strategies related to each other and remember their previous confrontation. Axelrod invited academic peers all over the world to design computer strategies and compete with each other in a repeated prisoner's dilemma competition. The differences in the participating procedures widely exist in these aspects: the complexity of the algorithm, the initial confrontation and the ability of forgiveness wait.
Axelrod found that when these confrontations were repeated for a long time by each participant who chose different strategies, judging from the perspective of self-interest, the final "greedy" strategy tended to decrease, while the more "altruistic" strategy was adopted. He used this blog

Who knows the meaning of this sentence All things have from, all things are form, and all from can be defined by number.

All things have form, all things are form, and all form can be defined by number

Understanding of zero (meaning in Mathematics) Talk about your understanding of zero! For example, the mathematical meaning of zero no longer means no or empty, and there are even more meanings. Please list at least 5. More is better,

Let me show you an interesting 0. If you ask a child in preschool or grade one, what does 0 mean? He will not hesitate to tell you that 0 means No. for example, there is no sheep on the grass. The teacher asked us to use 0. In the morning, my father bought me two apples, I ate one, and my brother ate one. Now one