课后测试(2)_opt
西瓜书课后习题——第二章
西⽠书课后习题——第⼆章2.1数据集包含500正例和500反例，按照70%的⽐例划分训练集和验证集，则验证集需要有150个正例、150个反例，则共有C1505002种划分⽅式。
2.2数据集包含100个样本，10折交叉验证时，每个训练集应该有45正例、45反例，验证集应该有5正例、5反例，由于训练集中正例、反例⽐例为1:1，则按照题⽬的预测算法，预测时会进⾏随机预测（因为训练样本数⽐例相同），所以错误率的期望为50%留⼀法时，留下来做验证集的样本有两种情况：正例、反例。
当留下来的是正例时，训练集中反例⽐正例多⼀个，按照题⽬的算法会将验证集预测为反例，预测错误；留下来的是反例时同理，会将验证集预测为正例。
所以错误率的期望为100%2.3F1的⼤⼩与BEP的⼤⼩没有明确的关系。
根据公式F1=2∗P∗RP+R，⽽BEP是查准率和查全率相等的点，即BEP=P=R，带⼊前式有F1=2∗P∗RP+R=2∗P∗PP+P=P=BEP，可以认为F1=BEP吗？显然不可以。
可以构造反例进⾏验证，容易构造BEP相同的两个分类器的F1值并不相同，分类器将所有训练样本按⾃⼰认为是正例的概率排序，排在越前⾯分类器更可能将它判断为正例。
按顺序逐个把样本标记为正，当查准率与查全率相等时，BEP=P=R。
当然分类器的真实输出是在这个序列中的选择⼀个位置，前⾯的标记为正，后⾯的标记为负，这时的查准率与查全率⽤来计算F1值。
可以看出有同样的BEP值的两个分类器在不同位置截断可能有不同的F1值，F1的⼤⼩与BEP的⼤⼩没有明确的关系。
2.4查全率：真正的正例被预测为正例的⽐率真正例率：真正的正例被预测为正例的⽐率显然查全率=真正例率查准率：预测的正例中真正的正例所占的⽐率假正例率：真正的反例被预测为正例的⽐率查准率与假正例率没有数值上的关系2.52.6ROC2.7参考图2.5由定义可以知道TPR与FPR都是由0上升到1，那么FNR则是由1下降到0。
Python核心编程第三版课后习题解答(第二章)
Python核心编程第三版课后习题解答——第二章2-1.面向连接的套接字和无连接的套接字之间的区别是什么？面向连接的：通信之前必须先建立起一个连接，提供序列化的，可靠的和不重复的数据交付，而没有边界记录。
无连接的：在通信开始之前并不需要建立连接，在数据传输过程中并无法保证它的顺序性，可靠性或重复性。
2-2.用自己的话描述客户端/服务器架构的意思。
服务器就是一系列硬件或软件，为一个或多个客户端（服务的用户）提供所需的“服务”。
它存在唯一目的就是等待客户端的请求，并响应它们（提供服务），然后等待更多的请求。
客户端因特定的请求而联系服务器，并发送必要的数据，然后等待服务器的回应，最后完成请求或给出故障的原因。
2-3.TCP和UDP之中，哪种类型的服务器接受连接，并将它们转换到独立的套接字进行客户端通信？TCP。
2-4.客户端。
更新Tcp和Udp客户端，以使得服务器名称无需硬编码到应用程序中。
此外，应该允许用户指定主机名和端口号，且如果二者中任何一个或者全部参数丢失，那么应该使用默认值。
[python]view plain copy1.<span style="font-family:'Comic Sans MS';font-size:18px;">from socket import *2.3.DefaultHOST = 'localhost'4.DefaultPORT = 12365.BUFSIZ = 10246.def GetAddr():7. Host = raw_input("Please input host:")8. Port = raw_input("Please input port:")9.return Host, int(Port)10.11.Host, Port = GetAddr()12.13.if not Host:14. Host = DefaultHOST15.if not Port:16. Port = DefaultPORT17.18.ADDR = (Host, Port)19.20.tcpCliSock = socket(AF_INET, SOCK_STREAM)21.tcpCliSock.connect(ADDR)22.23.while True:24. data = raw_input('> ')25.if not data:26.break27. tcpCliSock.send(data)28. data = tcpCliSock.recv(BUFSIZ)29.print data30.31.tcpCliSock.close()</span><span style="font-family:'Microsoft YaHei';font-size:24px;"><strong>32.</strong></span>2-5.网络互接和套接字。
第5章课后习题
第5章课后习题2．假设一条指令的执行过程分为"取指令"、"分析"和"执行"三段，每一段的时间分别为Dt、2Dt和3Dt。
在下列各种情况下，分别写出连续执行n条指令所需要的时间表达式。
(1) 顺序执行方式。
(2) 仅"取指令"和"执行"重叠。
(3) "取指令"、"分析"和"执行"重叠。
3．用一条5个功能段的浮点加法器流水线计算F＝。
每个功能段的延迟时间均相等，流水线的输出端与输入端之间有直接数据通路，而且设置有足够的缓冲寄存器。
要求用尽可能短的时间完成计算，画出流水线时空图，计算流水线的实际吞吐率、加速比和效率。
4．设有一个15000条指令的程序在一台时钟速率为25MHz的线性流水线处理机上执行。
假设该指令流水线有5段，并且每个时钟周期发射一条指令。
忽略由于转移指令和无序执行造成的损失。
(1) 用该流水线执行这一程序，并用流过延迟与其相等的一个等效非流水线处理机执行同一程序，将两者加以比较，并计算其加速比。
(2) 该流水线处理机的效率是多少？(3) 计算该流水线的吞吐率。
5．设有5段流水线处理机的预约表如下：(1) 列出禁止等待时间和冲突向量集。
(2) 画出状态转换图，说明不引起流水线冲突的所有可能的启动序列（循环）。
(3) 根据状态图列出所有简单循环。
(4) 从简单循环中找出迫切循环。
(5) 此流水线的最小平均等待时间(MAL)是多少？(6) 使用此流水线时，列出可允许的最小恒定循环。
(7) 该流水线的最大吞吐率是多少？(8) 如果使用最小恒定循环，则吞吐率是多少？1 2 3 4 5 6S1 X XS2 X XS3 XS4 XS5 X X6．下列汇编代码在一台3段流水线处理机上执行，每一段都有冒险(相关)检测和分解。
这三段是取指令、取操作数（根据要求取一个或者多个）和执行（包括写回操作）。
OPT 常问问题
Office of CommunicationsQuestions and Answers April 4, 2008USCIS ANNOUNCES NEW RULE ALLOWING EXTENSION OF OPTIONAL TRAINING PROGRAM FOR QUALIFIED STUDENTSRule Expands “Cap-Gap” Relief for Students with Pending H-1B PetitionsPRIOR F-1 REGULATIONS RELATING TO PRACTICAL TRAINING:What is optional practical training?Optional Practical Training (OPT) is temporary employment that is directly related to an F-1 student’s major area of study. Under existing rules, an F-1 student may be authorized to receive up to 12 months of practical training either pre- and/or post- completion of studies.•Pre-completion OPT:An F-1 student may be authorized to participate in pre-completion OPT after he/she has been enrolled for one full academic year. The pre-completion OPT must be directly related to the student’s course of study.Students authorized to participate in pre-completion OPT must work part-time while school is in session.They may work full time when school is not in session.•Post-completion OPT:An F-1 student may be authorized to participate in post-completion OPT upon completion of studies. The post-completion OPT must be directly related to the student’s course of study.What is the application process to participate in pre- or post-completion OPT?•Students must initiate a request by having their Designated School Official (DSO) recommend the OPT by endorsing Form I-20 and by making the appropriate notation in SEVIS, the system used to track F-1academic students.•Students then file Form I-765, Application for Employment Authorization Document (EAD), with USCIS. If approved, the student will be issued an EAD.•The student may begin engaging in pre- or post-completion OPT once an application has been approved and an EAD has been issued.How many students stand to benefit from today’s announcement?•There are approximately 26,000 students on OPT that have earned a bachelor's, master's, or doctorate in a STEM field. ICE and USCIS estimate that approximately 12,000 will take advantage of the STEMextension. Some of these students will be selected for an H-1B to start October 2009. Others may choose to continue their education, while some will depart the United States.•We estimate another 10,000 students will benefit from the automatic "cap gap" extension.What is the maximum duration of post-completion OPT?•Under the new rule, certain students will be eligible to receive a 17 month STEM extension of post-completion OPT.Do the periods of pre-completion OPT count against the available periods of post-completion OPT?•Yes. All periods of pre-completion OPT are deducted from the available periods of post-completion OPT.Are there fees associated with filing for extended OPT?•Yes. USCIS charges $380.00 when an applicant files an I-765 for optional practical training. CURRENT H-1B/CAP GAP REGULATIONS FOR F-1 ACADEMIC STUDENTS:What is the H-1B cap?•The cap is the Congressionally-mandated limit on the number of individuals who may be granted H-1B status during each fiscal year. For FY08, the cap is 65,000.What is the cap-gap?•Cap-gap occurs when an F-1 student’s status and work authorization expire in the current fiscal year, before they can start their approved H-1B employment in the next fiscal year beginning on October 1. An F-1 student in a cap-gap situation would have to leave the United States and return at the time his or her H-1B status becomes effective at the beginning of the next fiscal year.How does cap gap occur?•Many employers file H-1B petitions on behalf of F-1 students after their post-completion OPT expires.An employer can not file, and USCIS could not approve, an H-1B petition submitted earlier than sixmonths in advance of the date of actual need for the beneficiary’s services or training.As a result, the earliest date that an employer can file an H-1B petition for consideration under the next fiscal year cap is April 1, for an October 1 employment start date. If that H-1B petition and theaccompanying change of status request are approved, the earliest date that the student may start approved H-1B employment is October 1.Consequently, F-1 students who are the beneficiaries of approved H-1B petitions, but whose periods of authorized stay (including authorized periods of post-completion OPT and the subsequent 60-daydeparture preparation period) expire before October 1, must leave the United States, apply for an H-1B visa at a consular post abroad, and then seek readmission to the United States in H-1B status.What are the current cap-gap regulations?•Current regulations address the cap gap by authorizing an extension of the student’s authorized stay, but they do not extend the student’s employment authorization. This extension was not automatic, whichmeant that a notice had to be published in the Federal Register announcing the extension.•When this Federal Register notice was published, the student’s authorized stay was extended, but not the employment authorization. This means the student can remain in the United States until October 1, when the approved H-1B employment can begin, but cannot work until then.•If a Federal Register notice is not published, the student must leave the United States, apply for an H-1B visa, and seek readmission to the United States in H-1B status.How is the cap-gap situation changed under the interim final rule?•F-1 academic students on post-completion OPT maintain valid F-1 status until the expiration of their OPT. Once that OPT has ended, they are authorized to remain in the United States for up to 60 days to prepare for departure.•This cap-gap extension automatically becomes effective when the H-1B cap has been reached and the student has an H-1B petition filed on his/her behalf during the acceptance period.•If the H-1B petition filed on behalf of the student is not selected during the acceptance period, the automatic extension terminates when USCIS announces completion of the random selection on its public web site.•If the H-1B petition filed on behalf of the student is selected during the acceptance period, the student may remain in the United States and continue working until the October 1 start date indicated on theapproved H-1B petition. The student may benefit from this provision only if he/she has not violatedhis/her status.What is covered and clarified under the interim OPT Rule?•F-1 academic students may now apply for post-completion OPT 90 days before their academic programs end and no later than 60 days after their academic programs end.•This allows F-1 students seeking post-completion OPT to apply during their 60-day departure preparation periods, in the same way that they are allowed to apply for H-1B status during their departure preparation periods.•This allows students to ensure that they meet graduation requirements before applying for post-completion OPT.Is there additional post-completion OPT available to students in the high-tech industry?•F-1 academic students who receive science, technology, engineering, and mathematics (STEM) degrees and who receive an initial grant of post-completion OPT, may apply for a 17-month extension for amaximum of 29 months of post-completion OPT.•This gives U.S. businesses two chances recruit these highly desirable graduates through the H-1B process. Who is responsible for the development of the designated list of STEM degrees?•The STEM Designated Degree Program List is based on the "Classification of Instructional Programs"developed by the U.S. Department of Education's National Center for Education Statistics.What are the eligible STEM degrees?•To be eligible for the 17-month OPT extension, a student must have received a degree in one of the following fields:•Computer Science Applications •Life Sciences•Actuarial Science •Mathematics•Engineering •Military Technologies•Engineering Technologies •Physical Sciences.•The STEM degree list is posted on /sevis.What are the eligibility requirements for the 17-month extension of post-completion OPT?•The student must have a bachelor’s, master’s or doctorate degree in a STEM field.•The employer must be enrolled in E-Verify.•The student must apply on time (at least 90 days before the current post-completion OPT expires).What is the E-Verify program?•The E-Verify program is an internet-based system operated by USCIS, in partnership with the Social Security Administration (SSA).•The E-Verify program currently is the best means available for employers to determine employment eligibility of new hires and the validity of their Social Security Numbers.•E-Verify electronically compares information contained on the Employment Eligibility Verification Form I-9 with records contained in SSA and DHS databases to help employers verify identity and employment eligibility of newly-hired employees.Is there a cost associated with employers participating in the E-Verify program?•No, E-Verify is a free, easy to use web-based system available to employers and in all 50 states, the District of Columbia, Puerto Rico, Guam, and the U.S. Virgin Islands.What is the application process for the 17-month STEM extension?•The student files Form I-765 with USCIS, Form I-20 endorsed by the DSO, a copy of the STEM degree, and the required application fee.•Form I-765 is being amended to require the student to indicate the degree and provide the employer’s E-Verify information.•Students who timely file their STEM extension applications with USCIS may continue working while their applications are pending for 180 days or the date of the decision, whichever date is earlier.•This interim extension minimizes disruption in the student’s employment and also ensures that employers will conduct the necessary employment eligibility re-verification.What must a student do after being granted the 17-month STEM extension?•The student must report to his or her DSO (by email, within 10 days) any change in:-Legal name;-Residential and mailing address;-E-mail address;-Employer name;-Employer address;-Job title or position;-Supervisor name and contact information;-Employment start-date; and-Employment end-date•The student must also report to his or her DSO every six months (by email), confirming the information listed above; even if there have been no changes.•The requirement to report continues if the student’s 17-month STEM extension is extended further by the automatic cap-gap extension.– USCIS –。
opt页面置换算法例题详解(一)
opt页面置换算法例题详解(一)OPT页面置换算法例题解析1. 引言页面置换算法是操作系统中用于管理虚拟内存的重要算法之一。
OPT（Optimal）算法是一种最佳的页面置换算法，它通过预测未来的访问情况，选择未来最长时间不会被访问的页面进行置换。
本文将通过一个例题来详细解释OPT算法的工作原理。
2. 例题描述假设一个进程的虚拟内存中有5个页面，分别编号为1、2、3、4、5。
设进程的页面访问序列为1、2、1、4、5、1、2、4、3、5。
物理内存中的页面数为3，初始时物理内存为空。
3. 解题步骤Step 1: 遍历页面访问序列，将每个页面的下一次访问时间记录下来。
•页面1的下一次访问时间是2•页面2的下一次访问时间是7•页面3的下一次访问时间是8•页面4的下一次访问时间是4•页面5的下一次访问时间是9Step 2: 依次访问页面，并进行页面置换。
•访问页面1，物理内存为空，将页面1放入物理内存。
•访问页面2，物理内存中只有页面1，将页面2放入物理内存。
•访问页面1，物理内存中已有页面1和页面2，无需置换。
•访问页面4，物理内存中已有页面1和页面2，将页面4放入物理内存，并移除最长时间不会被访问的页面。
•访问页面5，物理内存中已有页面1、2和4，将页面5放入物理内存，并移除最长时间不会被访问的页面。
•访问页面1，物理内存中已有页面2、4和5，无需置换。
•访问页面2，物理内存中已有页面2、4和5，无需置换。
•访问页面4，物理内存中已有页面2、4和5，无需置换。
•访问页面3，物理内存中已有页面2、4和5，将页面3放入物理内存，并移除最长时间不会被访问的页面。
•访问页面5，物理内存中已有页面4、3和5，无需置换。
4. 结果分析根据以上步骤，使用OPT算法得到的页面置换序列为：1、2、X、4、5、X、X、X、3、X，其中X表示发生页面置换。
经过计算，OPT算法的页面命中次数为6次，缺页次数为4次。
OPT（最佳）页面置换算法是一种理论上的最优算法，可以最大程度地减少缺页次数。
2024年Python性能测试习题及答案整理,针对测试开发工程师的面试题集锦
Python性能测试_习题及答案解析（答案见尾页）一、选择题1. 性能测试的定义是什么？A. 性能测试是评估软件系统在特定负载下的响应速度和稳定性B. 性能测试是在正常负载下评估软件系统的响应速度和稳定性C. 性能测试是在高负载下评估软件系统的响应速度和稳定性D. 性能测试是在特定环境下评估软件系统的响应速度和稳定性2. Python 中常用的性能测试工具有哪些？A. timeit, cProfile, coverageB. timeit, memory-profiler, pytestC. timeit, cProfile, pytestD. timeit, memory-profiler, coverage3. 在进行性能测试时，以下哪种行为有助于找到性能瓶颈？A. 对代码进行详细的检查和分析B. 增加更多的代码以增加负载C. 监控系统的运行状况并收集日志D. 直接修改代码以提升性能4. 内存泄漏的定义是什么？A. 内存泄漏是指程序在运行过程中分配的内存无法被回收B. 内存泄漏是指程序在运行过程中释放的内存被重新分配C. 内存泄漏是指程序在运行过程中使用的内存超过预期D. 内存泄漏是指程序在运行过程中未分配的内存5. 以下哪个方法可以用来监控CPU的性能？A. timeitB. cProfileC. memory-profiler6. 下列哪种操作会导致磁盘IO性能下降？A. 将大量数据存储在内存中B. 将大量数据存储在磁盘上C. 使用磁盘缓存D. 将数据多次读取到内存中7. 以下哪种方法可以用来检测网络性能问题？A. timeitB. cProfileC. pytestD. netcat8. 下列哪种技术可以用来优化数据库性能？A. 索引B. 缓存C. 分库分表D. all of the above9. 在进行性能测试时，以下哪种行为可能会影响测试结果的准确性？A. 测试环境的配置相同B. 测试数据的规模较小C. 测试数据的规模较大D. 测试环境的配置不同10. 下列哪种方法可以通过检查代码执行的路径来定位性能瓶颈？A. timeitB. cProfileC. coverageD. pytest11. 下列哪个操作可以用来查看Python进程的内存使用情况？B. ctopC. topD. htop12. 在Python中，可以通过什么方法来检测内存泄漏？A. 使用局部变量B. 使用全局变量C. 使用collections库中的namedtupleD. 遍历所有变量并进行检查13. 下列哪种磁盘IO操作可以提高性能？A. 随机读写B. 顺序读写C. 大量连续读写D. 小文件随机读写14. 下列哪种情况下，应该对数据库进行优化？A. 数据库连接数较少B. 数据库表结构复杂C. 数据库查询语句简单D. 数据库数据量较小15. 下列哪种方法可以用来诊断CPU性能瓶颈？A. 只查看CPU使用率B. 查看CPU的使用情况分布C. 监控系统负载D. 分析内存占用情况16. 下列哪些操作可以帮助减少代码中的内存泄漏？A. 及时释放不再使用的对象B. 使用局部变量而非全局变量C. 使用字典而非列表D. 避免使用循环17. 在Python中，如何提高网络性能？A. 增加网络带宽B. 减少网络延迟C. 优化代码中的网络IO操作D. 所有上述方法18. 下列哪种情况下，应该对操作系统内核参数进行调整？A. 系统资源丰富B. 系统资源紧张C. 系统运行稳定D. 没有明显影响19. 下列哪些操作可以帮助优化数据库查询性能？A. 对数据库表进行索引B. 使用连接池管理数据库连接C. 减少数据库表数据量D. 分析并优化数据库查询语句20. 下列哪种情况下，可以考虑使用异步编程来提高程序性能？A. 需要频繁访问数据库B. 计算密集型任务较多C. 网络IO操作较为复杂D. 所有上述情况21. 性能优化的基本目标是提高系统的()。
otsu计算题
otsu计算题
以下是使用OTSU算法进行阈值处理的计算题：
题目：假设有一幅图像，像素灰度值范围是0-255，灰度级数为256，像素值是按照灰度值进行量化得到的。
现在我们需要使用OTSU算法来计算最佳阈值，将图像二值化。
解题步骤：
1.统计灰度级中每个像素在整幅图像中的个数，得到每个像素值的概率分布P(i)，其中i表示灰度值，P(i)表示灰度值为i的像素在图像中出现的概率。
2.遍历所有可能的阈值T（从0到255），将像素值小于T的像素归为前景类，像素值大于T的像素归为背景类。
3.计算当前阈值T下前景类和背景类的平均灰度值。
前景类的平均灰度值为Σ(i<T)*P(i)/N1，背景类的平均灰度值为Σ(i>=T)*P(i)/N2，其中N1和N2分别为前景类和背景类的像素个数。
4.计算当前阈值T下前景类和背景类的方差。
前景类的方差为Σ((i<T)*P(i)-(μ1)^2)，背景类的方差为Σ((i>=T)*P(i)-(μ2)^2)，其中μ1和μ2分别为前景类和背景类的平均灰度值。
5.计算类间方差。
类间方差为N1*N2*(μ1-μ2)^2，即前景类和背景类的方差之和。
6.遍历所有可能的阈值T，找到使类间方差最大的阈值T0，
即为最佳阈值。
7.根据最佳阈值T0，将像素值小于T0的像素归为前景类，像素值大于T0的像素归为背景类，从而实现图像的二值化。
Python程序设计课后习题答案第二单元
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