lecture6-tfidf
学术英语写作Unit 6.Introduction(课堂PPT)
In sentence 4 the writer describes the general problem area or the current research focus of the field.
8
In sentence 5 the writer provides a transition between the general problem area and the literature review.
10
➢ round
1. Polylactide (PLA) has received much attention in recent years due to its biodegradable properties, which offer important economic benefits. 2. PLA is a polymer obtained from corn and isproduced by the polymerization of lactide. 3. It has many possible uses in the biomedical field1 and has also been investigated as potential engineering material.2,3 4. However, it has been found to be too weak under impact to be used commercially.4
TFIDF算法在文章推荐系统的应用
TFIDF算法在文章推荐系统的应用作者：刘展来源：《电脑知识与技术》2019年第07期摘要：构建文章推荐系统需要把文章向量化，然后组建一个推荐矩阵，矩阵里的元数据（数值）会影响推荐效果，如何使文章推荐矩阵元数据更好地与用户行为关联起来，这里提出了基于TFIDF算法关联到用户行为的表示和更新机制，根据用户行为的特点，给予不同的权重，最终会影响到元数据的取值，进而能量化用户行为标签的兴趣值，另一方面也能产生更好的推荐效果。
关键词：TFIDF算法；余弦相似度；文章推荐系统；推荐矩阵；数据建模中图分类号：TP391 文献标识码：A文章编号：1009-3044（2019）07-0017-04Abstract： Static Building the article recommendation system needs to vectorize the article，and then form a recommendation matrix. The metadata （value） in the matrix will affect the recommendation effect. How to make the article recommendation matrix metadata better correlated with user behavior， here is based on TFIDF， The algorithm is associated with the representation and update mechanism of the user's behavior. According to the characteristics of the user's behavior，different weights are given， which ultimately affects the value of the metadata， thereby enlightening the interest value of the user's behavior tag， and on the other hand， it can produce better recommended effect.Key words： TFIDF algorithm； cosine similarity； article recommendation system；recommendation matrix；data modeling1 背景與意义随着移动互联网的发展和智能手机的广泛普及，越来越多的人选择在智能手机端或者平板设备上阅读，网络中的资源数量增长非常迅猛，比如微博、微信公众号、各种自媒体等，在海量资源用户面前，用户很难从中找到自己真正感兴趣的内容，或者要耗费大量的时间和精力才能找到自己所需要的资源。
Lecture_6
Galilean velocity transformation equation
Inertial frames of reference S' is moving at a velocity u with respect to another inertial frames of reference S.
2-3-2 Galilean principle of relativity
Galileo’s observation and understanding of the motion suffered two limitations: • within the realm of mechanics • the mechanical motions at very low speed: v « 299,792,458 meters per second Both of these two factors have greatly influenced Galileo’ s view of space and time and hence his concept of the principle of relativity.
The rigorous expression of the velocity transformation
dr dR dr ′ dR dr ′ dt ′ dt ′ v= = + = + ⋅ = u + v′ dt dt dt dt dt ′ dt dt
Galileo’s velocity transformation demands dt/dt’= 1, or
∆t = ∆t′
The central idea of Galileo’s concept of time: The time is absolute, the time interval is not rested upon the choice of the frame of reference.
tfidf 英文相似的计算
tfidf 英文相似的计算TF-IDF (Term Frequency-Inverse Document Frequency) is a commonly used method for calculating the similarity between English texts. Here's how you can compute the similarity using TF-IDF:1. Preprocessing: First, preprocess the texts by removing stop words, punctuation, and applying stemming or lemmatization to normalize the words.2. Building the Corpus: Create a collection of documents that you want to compare. Each document should be represented as a list of preprocessed words.3. Calculating TF-IDF: Calculate the TF-IDF score for each word in the corpus. TF-IDF is calculated by multiplying the term frequency (TF) of a word in a document by the inverse document frequency (IDF) of that word across the entire corpus.- Term Frequency (TF): Measures the frequency of a word within a document. It can be calculated by dividing the number of occurrences of a word in a document by the total number of words in that document.- Inverse Document Frequency (IDF): Measures the rarity of a word in the corpus. It can be calculated by taking the logarithm of the total number of documents divided by the number of documents containing the word, and then adding 1 to the result.4. Vectorization: Represent each document as a TF-IDF vector. The TF-IDF vector is a numerical representation of the document, where each dimension corresponds to a unique word in the corpus, and the value represents the TF-IDF score of that word in the document.5. Similarity Calculation: Finally, calculate the similarity between two documents using cosine similarity. Cosine similarity measures the cosine of the angle between two TF-IDF vectors, and it ranges from 0 (completely dissimilar) to 1 (completely similar).- Cosine Similarity: It can be calculated by taking the dot product of the TF-IDF vectors of two documents and dividing it by the product of their Euclidean norms.By following these steps, you can compute the similarity between English texts using TF-IDF. This method helps to identify the similarity or relatedness between different documents, which can be useful in various natural language processing tasks like information retrieval, document clustering, andrecommendation systems.。
lecture6(ch6)
Irwin/McGraw-Hill
©The McGraw-Hill Companies, Inc.,2001
6- 11
Net Present Value
Example - continued If the building is being offered for sale at a price of $350,000, would you buy the building and what is the added value generated by your purchase and management of the building?
16,000 16,000 466,000 NPV = −350,000 + + + 1 2 3 (1.07 ) (1.07 ) (1.07 ) NPV = $59,323
Irwin/McGraw-Hill
©The McGraw-Hill Companies, Inc.,2001
6- 12
Other Investment Criteria
©The McGraw-Hill Companies, Inc.,2001
6- 2
Topics Covered
Net Present Value Other Investment Criteria Project Interactions Capital Rationing
Irwin/McGraw-Hill
Internal Rate of Return
200 150 100 NPV (,000s) 50 0 -50 -100 -150 -200 Discount rate (%) 0 5 10 15 20 25 30 35
lecture6
How to Solve Mathematical Programs?
Graphically: This gives you a feel of what is happening By hand using a systematic analytical method Use your software such as Xpress-MP, GAMES, LINDO, CPLEX, Excel: • Software tools are computer implementations of systematic methods There are also specialized software for some transportation applications • Examples: TRANSCAD and EMME/2 for static traffic assignment (We have licenses of these software systems in the CTS Computing lab)
Link 2, x2 5
O D
5
t 2 ( x2 ) = 1 + 2 x2 t1 ( x1 ) = 2 + x1
Link 1, x1
t1
t2
t2 ( x2 )
Minimum of ( ∫ t1 ( w) dw + ∫ t 2 ( w) dw)
0 0
x1
x2
t1 ( x1 )
x2
1.225, 11/19/02
1.225, 11/19/02 Lecture 6, Page 4
[北科大]通用学术英语1 Unit6 Mini-lecture
Unit6Lecture 1 Critical thinking1.What is synthesis?The act of combining separate things into a coherent whole.2.What is necessary to synthesize?Synthesis is necessary to evaluate, compare, or explain relationships between several texts.3.When you read about a topic, what is significant for you to synthesize the texts about this topic? Searching for the flaws, weaknesses, or limitations and any potential links between various sources.4.When synthesizing existing literature, what is your aim and what are you expected to do?To provide an overview of the current state of knowledge about the research topic.To critically evaluate this bank of information, to identify themes and gaps and then synthesize this to provide the reader with a better understanding of the topic.Lecture 2 Reading5.What are the two types of synthesis essay? And what are their goals?○1Explanatory synthesis essay: mainly aims to convey information about a topic in order to help the reader understand that topic○2Argumentative synthesis essay: is not to explain, but to argue6.What is the difference between summery and synthesis?A summary is a recap or restatement of the important information of the source. The ideas, information and arguments of each source are stated in a concise manner.A synthesis on the other hand goes beyond a mere summary by critically evaluating the information. It should include a critical analysis of the relationship between different sources and it should relate to the sources to the author’s own research.7.What are effective methods of developing synthesis?○1the elementary synthesizing: proceed from a summary of the most relevant sources○2TWO REASONS approach: first of all, state your thesis, and then offer one or more reasonsLecture 3 Listening8.How to organize the sources thematically?○1three ways can be used collaboratively○2organize according to different opinions9.What are the ways of organizing a literature review?○1organize the sources around ideas, topics, or issues○2organize sources thematically○3arrange chronologically or methodologicallyLecture 4 Writing10.What is concession?Acknowledging a point made by the opposition before arguing one’s own point of view. Indicates an understanding of exactly what cause the controversy.Demonstrates maturity in thinking by considering the issue from other perspectives.11.Please list some concession words or phrases.although, even though, regardless of, while or despite12.Please list some contrasting conjunctions.but, however or whereas13.How to construct a concession?○1precede the thesis statement itself○2ensure that readers remember your idea most vividly○3prepare the reader for the next paragraph, which is likely to begin with a topic sentence that supports the thesis14.What is a concession-and-rebuttal consisted of?Concession, rebuttal and support of the claim in the rebuttal.15.Can you give an example of a concession-and-rebuttal?Lecture 5 Grammar: concession words and phrases16.What are the adverbs that can show contrast and concession?conversely, alternatively, granted, nonetheless, naturally, notwithstanding, obviously, instead 17.What are the phrases that can indicate contrast and concession?‘even if’, ‘even though’, ‘in contrast’, ‘I concede that’, ‘no doubt’。
Lecture06_CoverageTesting
Lecture 6 : Coverage TestingLiu YingBeijing Jiao Tong UniversityTesting, When is it enough?Copyright@2012 Software Testing2teacher.ying.liu@What We Need?●A way to know how much test has been performed. Thus a test coverage can be rule of thumb to determine the quality of software.●Code coverage is a measure used in software testing. It describes the degree to which the source code of a program has been tested. It is a form of testing that inspects the code directly and is therefore a form of white box testing.Copyright@2012 Software Testing3teacher.ying.liu@Code Coverage History●Code coverage techniques were amongst thefirst techniques invented for systematicsoftware testing. The first published reference was by Miller and Maloney inCommunications of the ACM in 1963.●Code coverage is one consideration in thesafety certification of avionics equipment. The standard by which avionics gear is certifiedby the Federal Aviation Administration (FAA) is documented in DO-178B.Copyright@2012 Software Testing4teacher.ying.liu@Code Coverage (cont.)●A way to try to cover more of the testing problem space so that we come closer to proving the absence of faults, or at least the absence of a certain class of faults.●It is ultimately expressed as a percentage (But the meaning of the percentage depends on what form of code coverage have been used.)Copyright@2012 Software Testing5teacher.ying.liu@How to Use Code Coverage in Testing Process?Copyright@2012 Software Testing6teacher.ying.liu@Where Does Code Coverage Fitinto The Testing Technique?●In black-box testing, we only use the specification to perform the test.●In white-box testing, we need to know that certain variables are designed to take values within a specific range●Code Coverage is a white-box testing methodology because code coverage requires knowledge of the code and looks into the code.Copyright@2012 Software Testing7teacher.ying.liu@Coverage Can Be Extended toBlack-box Testing●Instead of base on code, it is possible to determine coverage based on specifications.●This is of course dependent on the specification languages used.●It is easier to come up with a set of coveragecriteria for more formal specification languages.●For example, it is easier to come up the coveragecriteria for a state model than the coveragecriteria for English specifications.Copyright@2012 Software Testing8teacher.ying.liu@Coverage Testing●覆盖率是用于度量测试完整性的一个手段。
邹为诚《综合英语教程(6)》(第3版)学习指南(Unit6)【圣才出品】
Unit 6一、词汇短语Opportunities and Challenges for ChinaVocabularypoise [] n. 沉着，泰然自若；平衡v.使平衡；使(头等)保持一定姿势【例句】She tried her best to poise herself. 她尽全力使身体保持平衡。
【搭配】oneself on one’s toes踮着脚尖保持平衡paradox [] n. 自相矛盾的事物(思想、言论等)【例句】There has been no satisfactory resolution of the paradox. 这个怪现象并没有得到令人满意的解决。
【助记】para旁边，dox观点——旁门左道的观点——矛盾的话。
spout [] n. 喷管，喷口，水柱，喷流v. 喷出；滔滔不绝地讲【例句】①Children dislike being spouted at by pompous teachers. 学生不喜欢听自命不凡的教师对他们夸夸其谈。
②Don t spout off big talk. 不要说大话。
【词组】up the spout在绝境中，化为乌有，无望；怀孕spout sth. (out/up) 喷出，涌出(液体)【助记】sp＝spill( v. 溢出)，out－喷出outskirts [] n. 郊区，郊外【例句】They live on the outskirts of Paris. 他们住在巴黎市郊。
【助记】out外，skirt裙子，s：裙子的外边——郊区。
toddle [] v. (尤指幼儿)摇摇摆摆地走【例句】We watched the little boy toddle up purposefully to the refrigerator. 我们看着那小男孩特意晃到冰箱前。
drab [] adj. 黄褐色的，浅褐色的；枯燥无味的【例句】Life was now drab compared with the more exciting life style overseas.比起海外那种更富有刺激的生活方式来，现在的生活显得了无生气。
Lecture Notes for UNIT 6
I. Text IntroductionJames Albert Michener, in this text, shows readers changes of American society in: politics, courtship and marriage, feminist; and also the existence of three serious problems in: school education, job opportunities and welfare, and housing for the young.Despite these problems, the writer feels confident that America has good prospects. He feels proud of his motherland, of the great American people, and of the unique American democratic system.II. Culture Notes1. Puritanism (Paragraph 3)the practices and doctrines of the Puritans who were members of a group of Protestants in 16th- and 17th-century England and 17th-century America who believed in strict religious discipline and called for the simplification of acts of worship. The movement was an attempt to remove Roman Catholic influences from the Church of England.Text Introduction | Culture Notes | Author | Structure2. balanced system of government (Paragraph 8)The concept refers to the three branches of the United States government — the legislative, the executive, and the judicial — that restrain and stabilize one another through their separated functions. The legislative branch, represented by the Congress, must pass bills before they can become law. The executive branch —namely, the president —can veto bills passed by the Congress, thus preventing them from becoming law. In turn, by a two-thirds vote, the Congress can override the president's veto. The Supreme Court may invalidate acts of the Congress by declaring them contrary to the Constitution of the United States, but the Congress can change the Constitution through the amendment process.III. AuthorJames Albert Michener(1907-1997), American writer, became known for the voluminous research he incorporates and makes accessible and interesting in his writings. His books typically provide a detailed discussion of the history and geography of specific regions. His wide ranging writing career began when his experiences during World War II provided the material for a book of short stories, Tales of the South Pacific (1947); for which he received the 1984 Pulitzer Prize in fiction.His other works include Sayonara (1954); Hawaii (1959); Chesapeake (1978); The Covenant (1980); Poland (1982); Texas (1985); and Alaska (1988); The Novel (1991); Recessional (1994); A Miracle in Seville (1995); The Bridge at Andau (1957); Iberia: Spanish Travels and Reflections (1968); A Michener Miscellany: 1950-1970 (1973); Michener's memoir, The World Is My Home (1992).IV. Structural AnalysisPart I(1) reality: Americans still follow many of the old ways, similarities far greater thandifferences.Part II(2-4) major changes in American society, and the writer’s attitudes towards the changesPart III(5-7) main problems in American society and their reasonsPart IV(8-9) why America has good prospects and why the American system has survived and should surviveSection Three Detailed ReadingHOW AMERICA LIVESJames Albert Michener1. Americans still follow many of the old ways. In a time of rapid change it is essential that we remember how much of the old we cling to. Young people still get married (2.41million couples last year as opposed to only 1.52 million in 1960). Of course, many do get divorced, but they remarry at astonishing rates. They have children, but fewer than before. They belong to churches, even though they attend somewhat less frequently, and they want their children to have religious instruction. They are willing to pay taxes for education, and they generously support institutions like hospitals, museums and libraries. In fact, when you compare the America of today with that of 1950, the similarities are far greater than the differences.2. Americans seem to be growing conservative. The 1980 election, especially for the Senate and House of Representatives, signaled a decided turn to the right insofar as political and social attitudes were concerned. It is as if our country spent the 1960s and 1970s jealously breaking out of old restraints and now wishes to put the brakes on, as cautious people often do after a binge. We should expect to see a reaffirmation of traditional family values, sharp restraints on pornography, a return to religion and a rejection of certain kinds of social legislation.3. Patterns of courtship and marriage have changed radically. Where sex was concerned, I was raised in an atmosphere of suspicion, repression and Puritanism, and although husky young kids can survive almost anything, many in my generation suffered grievously. Without reservation, I applaud the freer patterns of today, although I believe that it's been difficult for some families to handle the changes.4. American women are changing the rules. Thirty years ago I could not have imagined a group of women employees suing a major corporation for millions of dollars of salary which, they alleged, had been denied them because they had been discriminated against. Nor could I imagine women in universities going up to the men who ran the athletic programs and demanding a just share of the physical education budget. But they are doing this — and with the support of many men who recognize the justice of their claims. At work, at play, at all levels of living women are suggesting new rules.5. America is worried about its schools. If I had a child today, I would send her or him to aprivate school for the sake of safety, for the discipline that would be enforced and for the rigorous academic requirements. But I would doubt that the child would get any better education than I did in my good public school. The problem is that good public schools are becoming pitifully rare, and I would not want to take the chance that the one I sent my children to was inadequate. Detailed Reading6. Some Americans must live on welfare. Since it seems obvious that our nation can produce all its needs with only a part of the available work force, some kind of social welfare assistance must be doled out to those who cannot find jobs. When I think of a typical welfare recipient I think of a young neighbor woman whose husband was killed in a tragic accident, leaving her with three young children. In the bad old days she might have known destitution, but with family assistance she was able to hold her children together and produced three fine, tax-paying citizens. I like that kind of social assistance and am willing to support it. America is essentially a compassionate society.7. America cannot find housing for its young families. I consider this the most serious danger confronting family life in America, and I am appalled that the condition has been allowed to develop. For more than a decade, travelers like me have been aware that in countries like Sweden, Denmark, Russia and India young people have found it almost impossible to acquire homes. In Sweden the customary wait was 11 years of marriage, and we used to ask, "what went wrong?" It seemed to us that a major responsibility of any nation would be to provide homes for its young people starting their families. Well, this dreadful social sickness has now overtaken the United States, and for the same reasons. The builders in our society find it profitable to erect three-bathroom homes that sell for $220,000 with a mortgage at 19 percent but find it impossible to erect small homes for young marrieds. For a major nation to show itself impotent to house its young people is admitting a failure that must be corrected.8. Our prospects are still good. I find our chances to be at least as good as those of any other nation and probably better. We have a physical setting of remarkable integrity, the world's best agriculture, a splendid wealth of minerals, great rivers for irrigation and an unsurpassed system of roads for transportation. We also have a magnificent mixture of peoples from all the continents with varied traditions and strengths. But most of all, we have a unique and balanced system of government.9. I think of America as having the oldest form of government on earth, because since we started our present democracy in 1789, every other nation has suffered either parliamentary change or revolutionary change. It is our system that has survived and should survive, giving the maximum number of people a maximum chance for happiness.I. AnalysisParagraph 1 AnalysisThe first paragraph is the introductory part of the essay. It mentions and illustrates the mainidea that Americans still follow many of the old ways though differences are obvious in American life. The last sentence tells us that a comparison of the America of today with that of 1950 shows that there are more similarities than differences.Detailed ReadingParagraphs 2-4 AnalysisThese three paragraphs, the second part of the essay, tell us about the major changes that have taken place and that are occurring in American life. From these paragraphs we get to know that Americans are growing conservative, that they have changed their patterns of courtship and marriage, enjoying much more freedom in these two aspects, and that American women are changing the old rules and suggesting new rules. After reading these three paragraphs, we can also have a clear idea of the writer's attitude towards these changes in American life. Obviously, he fully supports and welcomes them.Paragraph 5-7 Analys isThese three paragraphs, the third part of the essay, point out the main problems in American society: American schools are not as good as before; Americans who cannot find jobs do not get sufficient welfare; America shows itself impotent to house its young people. From these paragraphs, we can also see the writer's opinions of these problems.Paragraph 8-9 AnalysisThese two paragraphs, the concluding part of the essay, draw our attention to the writer's opinions of the nation's prospects and its system. It is worth noting that the writer provides good reasons for his opinions. From the conclusion, we can also get to know that the writer feels proud of his motherland and thinks highly of the American people and particularly the American system.II. Questions for ParagraphsParagraph 1: Questions1. Which sentences in this part show the main similarities and differences between American life in the present and that in the past?The following sentences show the main similarities and differences. "Young people still get married (2.41million couples last year as opposed to only 1.52 million in 1960). Of course, many do get divorced, but they remarry at astonishing rates. They have children, but fewer than before. They belong to churches, even though they attend somewhat less frequently, and they want their children to have religious instruction. They are willing to pay taxes for education, and they generously support institutions like hospitals, museums and libraries."2. In what ways are Americans generous?They are always ready to pay taxes for education, and they generously support institutions like hospitals, museums and libraries.Paragraph 2-4: Questions1. According to this part, what major changes have taken place or are taking place in Americansociety? Give an account of them.First of all, Americans are growing conservative in terms of their political and social attitudes. In the 1960s and 1970s, Americans broke out of old restraints. But the 1980 election, especially for the Senate and House of Representatives, signaled a decided turn to the right insofar as political and social attitudes were concerned. Since the beginning of the 1980s, Americans have become more conservative.Secondly, patterns of courtship and marriage have changed radically. When the author was a child, there prevailed an atmosphere of suspicion, repression and Puritanism, and many people in his generation suffered grievously. Now people enjoy much more freedom in terms of courtship and marriage. Thirdly, American women, who are no longer discriminated against, are changing the old rules. For example, they are bold enough to sue a major corporation for millions of dollars of salary which has been denied them. And women in universities are courageous enough to go up to the men who run the athletic programs and demand a just share of the physical education budget. All this was unimaginable in the past. Nowadays, at work, at play, at all levels of life, women are suggesting new rules.2. Pick out the sentences that indicate the writer's positive attitude towards the changes.1) "We should expect to see a reaffirmation of traditional family values, sharp restraints on pornography, a return to religion and a rejection of certain kinds of social legislation." This sentence implies that the writer welcomes changes towards the traditional values and beliefs. 2) "Without reservation, I applaud the freer patterns of today" This sentence tells us that the writer warmly welcomes the freer patterns of courtship and marriage in contemporary American life. 3) “demanding a just share of the physical educat ion budget. But they are doing this — and with the support of many men who recognize the justice of their claims. From his use of "a just share" and "the justice of their claims", we can infer that the writer fully supports American women who are changing the rules.Paragraph 5: QuestionWhat does the writer think of American schools?James Albert Michener thinks that American schools are not as good as they once were. According to him, public schools are not very safe, they are not very strict with their pupils, and they do not set rigorous academic demands on them. In his opinion, good public schools are becoming pitifully rare, and private schools do not provide satisfactory education, either, though they are better than public schools.Paragraph 6: QuestionDoes the writer applaud social assistance to the poor and the jobless? Support your answer by quoting the relevant sentences.Yes, he does. Clearly, he strongly advocates that social assistance be further promoted in America, which can be seen from the following sentences: "Some Americans must live on welfare. Since it seems obvious that our nation can produce all its needs with only a part of the available work force, some kind of social welfare assistance must be doled out to those who cannot find jobs? I like that kind of social assistance and am willing to support it."Paragraph 7: Questions1. Why cannot America find accommodation for its young married couples?Because the builders find it profitable to erect three-bathroom homes that sell for $220,000 with a mortgage at 19 percent, but they find it impossible to erect small homes for young married couples. In other words, the builders in American society do not want to build small homes for young married people because the building of small homes is less profitable.2. What is the writer's attitude towards the young people's housing problem in America?The writer considers the housing problem the young Americans are faced with to be the most serious danger confronting family life in America, and he is appalled that the condition has been allowed to develop. In his opinion, for a great nation like America to show itself impotent to house its young people means that it admits a failure that must be corrected.Paragraph 8: QuestionWhy does the writer say that America has good prospects despite its problems?He believes that America has chances that are at least as good as those of any other nation and probably better, and that Americans have a physical setting of remarkable integrity, the world's best agriculture, a splendid wealth of minerals, great rivers for irrigation and an unsurpassed system of roads for transportation. America boasts a magnificent blend of peoples from all the continents with varied traditions and strengths, and that most of all, America has a unique and balanced system of government.Paragraph 9: QuestionWhy has the American system survived and why should it survive?Because, according to the writer, the American system of government is a truly democratic system; it has not experienced either parliamentary change or revolutionary change; moreover, it offers the maximum number of people a maximum chance for happiness.III. Language Work of ParagraphsParagraph 1“In a time of rapid change it is essential that we remember how much of the old we cling to.” Paraphrase: In a time of quick transformation it is necessary for us to remember how many of the old ways we still adhere to.cling (on) to sb. or sth.: to hold on tightly to sb. or sth.; be unwilling to abandon it or refuse to give it up; become attached to it or stick to ite.g. T he rescuers saw the survivors clinging to a raft.She clung to the hope that he was still alive.Don't cling to the curb when you are driving.“They belong to churches, even though they att end somewhat less frequently, and they want their children to have religious instruction.”Paraphrase:They belong to particular groups of Christians, even though they attend religiousservices a bit less often, and they want their children to receive religious instruction.Paragraph 2“Americans seem to be growing conservative.”Paraphrase: Americans seem to be increasingly opposed to great or sudden changes. conservative adj. in favor of preserving the status quo and traditional values and customs, and against abrupt changese.g. H e made a conservative guess of the floating population in Shanghai.Is it true that old people are usually more conservative than the young?“The 1980 election, especially for the Senate and House of Representatives, signa led a decided turn to the right insofar as political and social attitudes were concerned.”Paraphrase: The 1980 election, especially for the Senate and House of Representatives, indicated a definite change to the right in terms of the voters' political and social attitudes.the Senate: the upper house of the law-making assembly in some countries, e.g. France, the USA, and Australiathe House of Representatives: the assembly of elected representatives in the central government of the USA, Australia and New Zealand“It is as if our country spent the 1960s and 1970s jealously breaking out of old restraints and now wishes to put the brakes on, as cautious people often do after a binge.”Paraphrase: It seems as though during the 1960s and 1970s we Americans made bold efforts to escape from old restrictions and now intend to put an end to it, just as cautious people often do after excessive indulgence.jealously adv. watchfully, carefullye.g. The publishing house is jealously protective of the copyright of all its books.restraint n. restriction, sth. that checks or controlse.g. I sharply feel the restraints of a limited income on the family budget.They imposed restraints on wage settlements.brake n. a device for reducing the speed of or stopping a car, bicycle, train, etc.; (fig.) restraint on sth.e.g. H is brakes failed on a steep hill.The Government is determined to put a brake on public spending.Ignorance acts as a brake to progress.binge n. (infml) time of wild eating and drinking; excessive indulgence in anythinge.g. H e went on a three-day binge.Business slowed down after a week-long shopping binge.“We should expect to see a reaffirmation of traditional family values, sharp restraints on pornography, a return to religion and a reject ion of certain kinds of social legislation.” Paraphrase: We hope and feel confident that traditional family values will be reaffirmed and pornography rigorously restricted, that those who have abandoned religion will come back to it, and that some kinds of social legislation will be turned down.reaffirmation n. an act of stating sth. positively againe.g. H is reaffirmation of loyalty impressed the Queen.His reaffirmation that he was ready to help touched our hearts.The government's reaffirmation of its principles caused strong responses from all thedeveloping countries.pornography n. describing or showing sexual acts in order to arouse sexual desires; books, films, plays, etc. that do this.e.g. Many people strongly believe that pornography is dehumanizing.The government launched a prohibition campaign against pornography.legislation n. action of making laws; the laws made.e.g. L egislation will be difficult and take time.Legislation is essential in every country.The major function of Congress is legislation.Paragraph 3“Patterns of courtship and marriage have changed radically.”Paraphrase: People have thoroughly changed the ways in which they date and marry.pattern n. the way in which sth. happens, moves, develops or is arranged; excellent examplee.g. S uch behavior patterns are not to be imitated.These sentences have the same grammatical pattern.The company's profit-sharing scheme set a pattern for others.courtship n. spending time together with a view to marriage; the period of romantic relationship before marriagee.g. They married after a brief courtship.Their long courtship ended in failure.“Where sex was concerned, I was raised in an atmosphere of suspicion, repression and Puritanism, and although husky young kids can survive almost anything, many in my generation suffered grievously.”Paraphrase: With regard to sex, I was brought up in an environment where suspicion, repression and Puritanism dominated. Although stoutly-built young people can endure almost anything, many people in my generation had awful experiences.repression n. restraining or suppressing; being restrained or suppressed; action of forcing desires and urges, esp. those in conflict with accepted standards of conduct, into the unconscious mind, often resulting in abnormal behaviore.g. His childhood was characterized by repression and solitude.They held a discussion about unhealthy sexual repression.Puritanism n. practices and beliefs of a Puritan, a person who is extremely strict in morals and who tends to regard pleasure as sinfule.g. Puritans strictly practice Puritanism.Puritanism is not very popular nowadays.husky adj. big and strong; dry in the throat, sounding slightly hoarsee.g. T hose basketball players are all husky young men.Our teacher is still a bit husky after his bad cold.“Without reservation, I applaud the freer patterns of today, although I believe that it's being difficult for some families to handle the changes.”Paraphrase: I fully praise or approve of the less rigid patterns of courtship and marriage today, despite the fact that, in my opinion, some families are finding it very hard to cope with these changes.Paragraph 3“Thirty years ago I could not have imagined a group of women employees suing a major corporation for millions of dollars of salary which, they alleged, had been denied them because they had been discriminated against.”Paraphrase:employees should sue a major company for millions of dollars of salary which was their due but was denied them by the corporation just because they were the "weaker sex".sue vt. make a legal claim (against sb.)e.g. The boss was sued for breaching the contract.The man is suing for a divorce.allege vt. state sth. as a fact without proof; give sth. as an argument or excusee.g. The prisoner alleged that he was at home on the night of the crime.He alleged illness as the reason for his absence.“Nor could I have imagined women in unive rsities going up to the men who ran the athletic programs and demanding a just share of the physical education budget.”Paraphrase:in charge of the sports plans, and ask for an equal share of the amount of money allotted for their physical education.athletic adj. of athletes or athletics; physically strong, healthy and activee.g. He often goes to an athletic club.He has an athletic figure.She looks very athletic.budget n. an estimate or plan of how money will be spent over a period of time, in relation to the amount of money available; amount of money needed or allotted for a specific purposee.g. I could not go to the restaurant with you because of my tight budget.She limits herself to a daily budget of ten pounds.A family on a budget cannot afford meat every day.“who recognize the justice of their claims”ParaphraseParagraph 3“If I had a child today, I would s end her or him to a private school for the sake of safety, for the discipline that would be enforced and for the rigorous academic requirements.” Paraphrase: Should I have a child of school age today, I would have him or her receive education at a private school, where security for kids is guaranteed, discipline is enforced, and strict scholastic expectations are placed on them.Note:It is necessary to note that this sentence is in the subjunctive mood. The sentence tells us indirectly that American private schools are safe, they impose strict discipline on their pupils, and that they set rigorous academic demands on them. Therefore, we readers could naturally come to the conclusion that American public schools are not very safe, they do not impose strict discipline, and that they have no rigorous academic requirements.rigorous adj. very strict; strictly accurate or detailede.g. She did not receive any rigorous training in athletics, but she got a prize at thesports meet.You must make a rigorous analysis of the text before you can translate it well.“But I would doubt that the child would get any better education than I did in my good public school.”Explanationin America today do not provide any better education than the good public school where he received education. In other words, the author believes that even private schools in America today cannot be compared with good public schools in the past in terms of the education quality.“The problem is that good public schools are becoming pitifully rare, and I would not want to take the chance that the one I sent my children to was inadequate.”Paraphrase ecoming fewer and fewer, and I would not run the risk of sending my kids to one of them.inadequate adj. not sufficient or enough; not good enough for a particular purpose; not sufficiently able or confident to deal with a difficult situatione.g. T hese security precautions are totally inadequate in face of terrorism.The war refugees have inadequate supplies.She felt inadequate when faced with so tough a task.Paragraph 6“Since it seems obvious that our nation can produce all its needs with only a p art of the available work force, some kind of social welfare assistance must be doled out to those who cannot find jobs.”Paraphrase:are needed to produce sufficient food and goods, etc. to meet the needs of all the American people, some kind of social welfare assistance must be provided for those who are not able tofind any jobs.dole sth. out: distribute (esp. food, money, etc.) in small amountse.g. Allowances are grudgingly doled out to the elderly.The donated money was doled out to the tsunami-stricken victims.a typical welfare recipient: a characteristic person that enjoys welfare assistance“In the bad old days she might have known destitution, but with famil y assistance she was able to hold her children together and produced three fine, tax-paying citizens.”Paraphrase: In the bad old days she might have experienced or lived in abject poverty, but with welfare assistance for poor families she managed to keep her three children under her care and nurtured them into worthy citizens that made contributions to their country.destitution n. in a state of poverty; in a condition of being impoverished; being without money, food, and other life necessitiese.g. There are still some people who live in complete destitution.After his death, his family was plunged into destitution.“America is essentially a compassionate society.”Paraphrase: America is, in its true nature, a society filled with pity for others' sufferings and inclined to help others.In other words, American people are very sympathetic by nature, and they are always ready to help others.compassionate adj. sympathetic; being filled with pity inclining one to help or to be merciful Detailed Readinge.g. Most people are compassionate beings, but there are some who never knowcompassion.The compassionate teacher showed lenience to the student who committed cheating for the first time.Paragraph 7“and I am appalled that the condition has been allowed to develop.”Paraphrase: and I am shocked that this dreadful condition should have been allowed to exist and deteriorate.appalled adj. very shocked and upset by sth. very bad or unpleasante.g. The newspaper reports about starving children appalled me.We were appalled at the prospect of having to miss our holiday.“Well, this dreadful social sickness has now overtaken the United States, and for the same reasons.”Paraphrase: Well, America has now been seized by this terrible social illness, and for the same reasons.Note:This sentence involves a case of metaphor: the terrible condition mentioned in the foregoing sentences is compared to a dreadful social illness。
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Bag of words model
Vector representation doesn’t consider the ordering of words in a document John is quicker than Mary and Mary is quicker than John have the same vectors This is called the bag of words model. In a sense, this is a step back: The positional index was able to distinguish these two documents. We will look at “recovering” positional information later in this course. For now: bag of words model
Consider the number of occurrences of a term in a document:
Each document is a count vector in ℕv: a column below
Antony and Cleopatra
Julius Caesar
The Tempest
This lecture; IIR Sections 6.2-6.4.3
Ranked retrieval Scoring documents Term frequency Collection statistics Weighting schemes Vector space scoring
Ch. 6
Ranked retrieval
Thus far, our queries have all been Boolean.
Documents either match or don’t.
Good for expert users with precise understanding of their needs and the collection.
collection (text, xml markup etc) collection (text) Term-doc incidence matrix postings, uncompressed (32-bit words) postings, uncompressed (20 bits) postings, variable byte encoded postings, g-encoded 3,600.0 960.0 40,000.0 400.0 250.0 116.0 101.0 MB
Free text queries: Rather than a query language of operators and expressions, the user’s query is just one or more words in a human language In principle, there are two separate choices here, but in practice, ranked retrieval models have normally been associated with free text queries and vice versa
Recall (Lecture 1): Binary termdocument incidence matrix
Antony and Cleopatra Julius Caesar The Tempest Hamlet
Sec. 6.2
Othello
Macbeth
Antony Brutus Caesar Calpurnia Cleopatra mercy worser
Introduction to Information Retrieval
Introduction to
Information Retrieval
Chapter 6: Scoring, Term Weighting and the Vector Space Model
1
ห้องสมุดไป่ตู้
Recap of last lecture
Ch. 6
When a system produces a ranked result set, large result sets are not an issue
Ch. 6
Scoring as the basis of ranked retrieval
We wish to return in order the documents most likely to be useful to the searcher How can we rank-order the documents in the collection with respect to a query? Assign a score – say in [0, 1] – to each document This score measures how well document and query “match”.
Ch. 6
Take 1: Jaccard coefficient
Recall from Lecture 3: A commonly used measure of overlap of two sets A and B jaccard(A,B) = |A ∩ B| / |A ∪ B| jaccard(A,A) = 1 jaccard(A,B) = 0 if A ∩ B = 0 A and B don’t have to be the same size. Always assigns a number between 0 and 1.
Ch. 6
Issues with Jaccard for scoring
It doesn’t consider term frequency (how many times a term occurs in a document) Rare terms in a collection are more informative than frequent terms. Jaccard doesn’t consider this information We need a more sophisticated way of normalizing for length Later in this lecture, we’ll use | A B | / | A B | . . . instead of |A ∩ B|/|A ∪ B| (Jaccard) for length normalization.
This is particularly true of web search.
Problem with Boolean search: feast or famine
Ch. 6
Boolean queries often result in either too few (=0) or too many (1000s) results. Query 1: “standard user dlink 650” → 200,000 hits Query 2: “standard user dlink 650 no card found”: 0 hits It takes a lot of skill to come up with a query that produces a manageable number of hits.
Collection and vocabulary statistics: Heaps’ and Zipf’s laws Dictionary compression for Boolean indexes Dictionary string, blocks, front coding Postings compression: Gap encoding, prefix-unique codes Variable-Byte and Gamma codes
Hamlet
Othello
Macbeth
Antony Brutus Caesar Calpurnia Cleopatra mercy worser
157 4 232 0 57 2 2
73 157 227 10 0 0 0
0 0 0 0 0 3 1
0 1 2 0 0 5 1
0 0 1 0 0 5 1
0 0 1 0 0 1 0
1 1 1 0 1 1 1
1 1 1 1 0 0 0
0 0 0 0 0 1 1
0 1 1 0 0 1 1
0 0 1 0 0 1 1
1 0 1 0 0 1 0
Each document is represented by a binary vector ∈ {0,1}|V|
Sec. 6.2
Term-document count matrices
Also good for applications: Applications can easily consume 1000s of results.
Not good for the majority of users.
Most users incapable of writing Boolean queries (or they are, but they think it’s too much work). Most users don’t want to wade through 1000s of results.