Thesecondeditionofthiswell-knownandhighlyregardedtextcanbeusedasthebasisforaone-ortwo-semesterundergraduatecourseinsignalsandlinearsystemstheoryandapplications.Topicsincludebasicsignalsandsystemsconcepts,lineartime-invariant(LTI)systems,Fourierrepresentationsofcontinuous-timeanddiscrete-timesignals,theCTandDTFouriertransforms,andtime-andfrequency-domainanalysismethods.Theauthoremphasizesapplicationsofthetheorythroughnumerousexamplesinfiltering,sampling,communications,andfeedback.Theparalleldevelopmentofcontinuous-timeanddiscrete-timefrequencydomainmethodsallowsthereadertoapplyinsightsandintuitionacrossthetwodomains.Italsofacilitatesadeeperunderstandingofthematerialbybringingintofocusthesimilaritiesanddifferencesbetweenthetwodomains.Thetextalsoincludesintroductorychaptersoncommunicationsystemsandcontroltheory.Thisbookassumesthatyouhaveabackgroundincalculusaswellasexposuretocomplexnumbersandelementarydifferentialequations.Becauseofitsthoroughnessandunhurriedpace,thistextishighlyrecommendedforstudentsandthoseinterestedinself-study.

Progressinsoftwareengineeringhasbeenremarkableovermyprofessionallifetime.Oursocietiescouldnotfunctionwithoutlarge,professionalsoftwaresystems.Forbuildingbusinesssystems,thereisanalphabetsoupoftechnologies—J2EE,.NET,SaaS,SAP,BPEL4WS,SOAP,CBSE,etc.—thatsupportthedevelopmentanddeploymentoflargeenterpriseapplications.Nationalutilitiesandinfrastructure—energy,communications,andtransport—allrelyoncomplexandmostlyreliablecomputersystems.SoftwarehasallowedustoexplorespaceandtocreatetheWorldWideWeb,themostsignificantinformationsysteminthehistoryofmankind.Humanityisnowfacedwithanewsetofchallenges—climatechangeandextremeweather,decliningnaturalresources,anincreasingworldpopulationtobefedandhoused,internationalterrorism,andtheneedtohelpelderlypeopleleadsatisfyingandfulfilledlives.Weneednewtechnologiestohelpusaddresstheseproblemsand,forsure,softwarewillplayacentralroleinthesetechnologies.Softwareengineeringis,therefore,acriticallyimportanttechnologyforthefutureofmankind.Wemustcontinuetoeducatesoftwareengineersanddevelopthedisciplinesothatwecancreatemorecomplexsoftwaresystems.Ofcourse,therearestillproblemswithsoftwareprojects.Softwareisstillsometimeslateandcostsmorethanexpected.However,weshouldnotlettheseproblemsconcealtherealsuccessesinsoftwareengineeringandtheimpressivesoftwareengineeringmethodsandtechnologiesthathavebeendeveloped.Softwareengineeringisnowsuchahugeareathatitisimpossibletocoverthewholesubjectinonebook.Myfocus,therefore,isonkeytopicsthatarefundamentaltoalldevelopmentprocessesandtopicsconcernedwiththedevelopmentofreliable,distributedsystems.Thereisanincreasedemphasisonagilemethodsandsoftwarereuse.Istronglybelievethatagilemethodshavetheirplacebutsotoodoes‘traditional’plan-dri

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在日常工作中，钉钉打卡成了我生活中不可或缺的一部分。然而，有时候这个看似简单的任务却给我带来了不少烦恼。 每天早晚，我总是得牢记打开钉钉应用，点击"工作台"，再找到"考勤打卡"进行签到。有时候因为工作忙碌，会忘记打卡，导致考勤异常，影响当月的工作评价。而且，由于我使用的是苹果手机，有时候系统更新后，钉钉的某些功能会出现异常，使得打卡变得更加麻烦。 另外，我的家人使用的是安卓手机，他们也经常抱怨钉钉打卡的繁琐。尤其是对于那些不太熟悉手机操作的长辈来说，每次打卡都是一次挑战。他们总是担心自己会操作失误，导致打卡失败。 为了解决这些烦恼，我开始思考是否可以通过编写一个全自动化脚本来实现钉钉打卡。经过一段时间的摸索和学习，我终于成功编写出了一个适用于苹果和安卓系统的钉钉打卡脚本。