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1、18SimpleexamplesToillustratetheprinciplessetoutinthepreviouschapterletusnowexaminetwosimpleexamples.Example1Forthefirstexampleletusconsidertherathermundaneoperationofgettingupinthemorning,andletuslookattheconstituentactivitiesbetweenthealarmgoingoffandboardingourt
2、raintotheoffice.ProjectPlanningandControlThelistofactivities–notnecessarilyintheircorrectsequence–isroughlyasfollows:Time(min)Aswitchoffalarmclock0.05Bliebackandcollectyourthoughts2.0Cgetoutofbed0.05Dgotothebathroom0.10Ewashorshower6.0Fbrushteeth3.0Gbrushhair3.0Hs
3、have(ifyouareaman)4.0Jboilwaterfortea2.0Kpourtea0.10Lmaketoast3.0Mfryeggs4.0Nservebreakfast1.0Peatbreakfast8.0Qcleanshoes2.0Rkisswifegoodbye0.10Sdoncoat0.05Twalktostation8.0Uqueueandbuyticket3.0Vboardtrain1.050.45Theoperationslistedabovecanberepresenteddiagrammati
4、callyinanetwork.ThiswouldlooksomethinglikethatshowninFigure18.1.Itwillbeseenthattheactivitiesarealljoinedinonelongstring,startingwithA(switchoffalarm)andendingwithV(boardtrain).Ifwegiveeachactivityatimeduration,wecaneasilycalculatethetotaltimetakentoperformthecomp
5、leteoperationbysimplyaddinguptheindividualdurations.Intheexamplegiven,thistotaltime–orprojectduration–is50.45minutes.Intheory,therefore,ifanyoperationtakesafractionofaminutelonger,wewillmissourtrain.Consequently,eachactivitybecomescriticalandthewholesequencecanbes
6、eentobeonthecriticalpath.Inpractice,however,wewillobviouslytrytomakeupthetimelostonanactivitybyspeedingupasubsequentone.Thus,ifweburnthetoastandhavetomakeanewpiece,wecanmakeupthetimebyrunningtothestationinsteadofwalking.Weknowthatwecandothisbecausewehaveabuilt-in1
7、36SimpleexamplesABCDEFG.052.05.1633HJKLMNP42.13418RSTUV2.1.05831Figure18.1marginorfloatinthejourneytothestation.Thisfloatis,ofcourse,thedifferencebetweenthetimetakentowalkandruntothestation.Inotherwords,thepathisnotascriticalasitmightappear,i.e.wehavenotinourorigi
8、nalsequence–ornetwork–paredeachactivitydowntoitsminimumduration.Wehadsomethingupoursleeve.However,letussupposethatwecannotruntothestationbecausewehaveab
