Vensim软件学习.ppt

Vensim软件学习.ppt

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Vensim软件介绍,界面及工具建立因果反馈图（causalloopdiagrams）和流图（StockandFlowDiagrams）模拟过程函数：

LOOKUP、TIME、STEP,WhatisVensim?

Vensimisavisualmodelingtoolthatallowsyoutoconceptualize,document,simulate,analyze,andoptimizemodelsofdynamicsystems.Vensimprovidesasimpleandflexiblewayofbuildingsimulationmodelsfromcausallooporstockandflowdiagrams.Byconnectingwordswitharrows,relationshipsamongsystemvariablesareenteredandrecordedascausalconnections.ThisinformationisusedbytheEquationEditortohelpyouformacompletesimulationmodel.Youcananalyzeyourmodelthroughoutthebuildingprocess,lookingatthecausesandusesofavariable,andalsoattheloopsinvolvingthevariable.Whenyouhavebuiltamodelthatcanbesimulated,Vensimletsyouthoroughlyexplorethebehaviorofthemodel.-VensimUsersGuideVersion5,界面及工具,标题TitleBar,菜单Menu,Toolbar,绘图工具SketchTools,状态条StatusBar,StructuralAnalysisToolsCausesTreecreatesatree-typegraphicalrepresentationshowingthecausesoftheWorkbenchVariable.因果树图UsesTreecreateatree-typegraphicalrepresentationshowingtheusesoftheWorkbenchVariable.使用树图LoopsdisplaysalistofallfeedbackloopspassingthroughtheWorkbenchVariable.反馈图Documentreviewsequations,definitions,unitsofmeasure,andselectedvaluesfortheWorkbenchVariable.DatasetAnalysisToolsCausesStripGraphdisplayssimplegraphsinastrip,allowingyoutotracecausalitybyshowingthedirectcauses（asshown）oftheWorkbenchVariable.显示与所选择变量有直接关系的变量的模拟结果GraphdisplaysbehaviorinalargergraphthantheStripGraph,andcontainsdifferentoptionsforoutputthantheStripGraph.TablegeneratesatableofvaluesfortheWorkbenchVariable.RunsComparecomparesallLookupsandConstantsinthefirstloadeddatasettothoseinthesecondloadeddataset.,分析工具,AnalysisToolOutput,控制板TheControlPanelTheControlPanelallowsyoutochangeinternalsettingsthatgoverntheoperationofVensim,suchaswhichWorkbenchVariableisselectedorwhatDatasetsareloaded.,2.建立因果反馈图（Causalloopdiagram）和建立流图（Stockandflowdiagram）,1）建立因果反馈图（causalloopdiagrams）：

以Savings-Interest为例,演示,3种分析工具：

CauseTree；UsesTree；Loops，分析因果反馈图的逻辑结构,两个图经由变量savings的因果关系而连接，刚好分别前后对调；当反馈环向后回到该变量，则用括号括起来。

确定savings为变量后，点击Loops,列举全部有关该变量的因果反馈图,LoopNumber1oflength1savinginterestLoopNumber2oflength2savingworkeffortincome,因果反馈图只能描述反馈结构的基本方面，不能表示不同性质的变量的区别，这是其根本弱点。

如状态变量的积累概念，是系统动力学中最重要的量，然而因果反馈图全然忽视了这一点。

因此，需要建立流图。

2）建立流图（StockandFlowDiagrams）-以workforce-inventory为例,constructInventoryasaLevel,thenaddarateflowinginandarateflowingout.,Nowweneedtofigureouthowproductiongetsdetermined.addthelevelWhireratecaneitherincreaseordecreasetheworkforce.,addtheproportionalityconstantproductivity.Also,nethirerateisdependentonthevalueofWorkforce.,addinthevariablestargetworkforceandtimetoadjustworkforceandconnectthem.,Addtheconceptoftargetproduction,andconnectittotargetworkforce.Wewillsettargetproductiononthebasisofsales.,introducetargetinventory,inventorycorrectionandtwoadditionalConstants.Theideaissimple.targetinventoryistheamountofstockthatshouldbeheldbasedonexpectationsaboutsales.TheinventorycorrectionisthecorrectionforadeviationofInventoryfromitstarget.,3.模拟：

以workforce-inventory为例,ThefollowingstepsaretypicalforbuildingandusingVensimmodels.Constructamodeloropenanexistingmodel.ExaminethestructureusingthestructuralAnalysistools（TreeDiagrams.）.Simulatethemodelmovingaroundmodelparameterstoseehowitresponds.ExamineinterestingbehaviorinmoredetailusingthedatasetAnalysistools（GraphsandTables）.Performcontrolledsimulationexperimentsandrefinethemodel.PresentthemodelanditsbehaviortoyouraudienceusingSyntheSimresults,AnalysistooloutputcustomerGraphsandTables.,1）openanexistingmodel:

c:

ProgramFilesVensimmodelsguidechap03WFINV.MDL,2）ExaminethestructureusingthestructuralAnalysistools（TreeDiagrams.）.,CausesTreeDiagram（WorkbenchVariable,Inventory,isontherightandeverythingthatcausesittochange（upto2connectionsdistant）isontheleft.）,theWorkbenchVariableontheleftandwhereitisusedinthemodel（whatitcauseschange,upto2connectionsdistant）ontheright.,UsesTreeDiagram,theLoopsAnalysistool:

variablenethirerate,LoopNumber1oflength1nethirerateWorkforceLoopNumber2oflength6nethirerateWorkforceproductionInventoryinventorycorrectiontargetproductiontargetworkforce,displaysallvariablesinallfeedbackloops（two）thatpassthroughtheWorkbenchVariable（nethirerate）.,3）SimulatingtheModel:

amountofInventoryovertime.,DoubleclickonthesimulationRunnameeditingboxontheToolbartohighlightthedefaultnameCurrent（orclickonceanddragoverthenameCurrent）,thentypeinthenamebaserun.ClickontheSyntheSimbutton,DoubleclickonthesimulationRunnameeditingboxontheToolbaragainandreplacethenamebaserunwithexperiment.,Usingthemousedragthesliderbelowproductivitybackandforth.Asyoumovethesliderthemodelwillsimulateandtheresultswilldisplayinblue,withtheresultsfrombaserunbeingshowninred.,4）ExaminingBehavior,PositionthemouseoverWorkforceandleaveitthere.Agraphshouldpopupjustbelowworkforce.,ClickonWorkforcetoselectitintotheWorkbench.ClickontheGraphAnalysistoolTwothingsareworthnotingabouttheabovegraph.Firstbothrunsshowapatternofbehaviorknownasdampedoscillation.Second,thetworunsareidenticalexceptforscaling.,ClickonthevariableInventoryappearinginthesketchandthenclickontheGraphtool,WeseeagraphofInventorywithoscillatingbehaviorsimilartoworkforce,althoughInventorystartsoutbydecliningbeforeincreasinginvalue.Moreimportantly,thereisonlyonegraphvisible.,ClickontheTabletool,OnlyonegraphlineisvisibleforInventorybecausethevaluesareidenticalforbothruns.ChangingproductivityimpactsonlyWorkforce,targetworkforceandnethirerate.Thisisquiteclearjustbylookingatthemodeldiagramasyoudragthesliderandoccursbecauseproductivityreallyjustscalesthenumberofpeoplerequiredtoproduceoneitem.,ClickontheResetSliderbuttonorpresstheHomekeytoreturnthevalueofproductivitytoitsoriginalsetting.Repeattheaboveexperimentationprocesswitheachofthethreeremainingconstants.Dragtheslidersobservingbehaviorandthenbringupmoredetailedgraphswhenyouseesomethinginteresting.,Thethingstobelookingforwhenyouareevaluatingbehavioraretheperiodofoscillation（振动）,theextentbywhichvariableschangeandthedegreeofdamping（衰减）.Theperiodofoscillationisthetimefromonepeaktothenextonthetimegraphs.Dampingisthedecreaseinamplitudethatoccursfrompeaktopeak,whereamplitudeisthedistancealongtheyaxisfromtheeventualvaluethevariablesettlesto.Itshouldbeeasytoseethatproductivityandinventorycoveragedonotsignificantlychangethesewhiletimetoadjustworkforceandtimetocorrectinventorydo.,timetoadjustworkforce,5）CausalTracing,JustasyoulookedatthecausesofInventorybyusingtheCausesTreeDiagramAnalysistool,youcanalsolookatgraphsofbehaviorofthevariablesthatcauseInventorytochange.,ClickontheResetAllbuttonorusethekeycombinationCtrl+Home.ClickonInventorytoselectitintotheworkbench.ClickontheCausesStripAnalysistool,AstripgraphisgeneratedthatshowstheWorkbenchVariable（Inventory）atthetop,andallthevariablesthatdirectlycauseInventorytochangebelowit（productionandsales）.wewilllookintoproductionandnotsalestounderstandthesourceofthisoscillation.,CausalTracingisaquickandpowerfultoolthathelpsusdeterminewhatportionsofamodelarecausingwhichtypesofbehavior.TheCausesandUsesTreeDiagramsandtheTabletoolcanallbeusedforCausalTracingbutthemostcommonlyusedtoolistheCausesStriptoolandwewillusethattoinvestigatethesourcesofoscillationinthismodel.,4.几个常用函数：

LOOKUP、TIME、STEP,1）LOOKUP：

说明在一个模拟模型中任意两个变量之间的函数关系；可以描述一个表格包含两个变量的一组值。

比如，改变原储蓄存款模型（Saving-Interest）。

当存款少于5000￥，利率为5；存款不少于5000￥，利率为7。

相当于原来DYNOMA中的table函数,演示,2）TIME变量一些Vensim功能明显是时间函数，为了使用这一功能，在模型中必须使用TIME当作函数。

比如，对某些产品100单位振幅与12个月季节变化需求。

时间以月为单位。

VariableDemand=100*sin（2*3.14159*Time/12）,演示,注意：

Time用符号包起来，表示它是一个隐藏式变量,3）STEP函数,阶跃函数产生一个从零到给定值的一次阶跃。

比如WFINV.MDL中sales=100+STEP（50,20）TheSTEPfunctionisoneofthemostcommonlyusedinputfunctions.Thisfunctionreturns0untilTimereachesstimeandthenitreturnssheight.Inourexampleitwillreturn0tilltime20thenitwillreturn50sothatsaleswillstartat100,remainconstanttilltime20andthenjumpto150.,Vensim软件介绍,界面及工具建立因果反馈图（causalloopdiagrams）和流图（StockandFlowDiagrams）模拟过程函数：

LOOKUP、TIME、STEP,WhatisVensim?

Vensimisavisualmodelingtoolthatallowsyoutoconceptualize,document,simulate,analyze,andoptimizemodelsofdynamicsystems.Vensimprovidesasimpleandflexiblewayofbuildingsimulationmodelsfromcausallooporstockandflowdiagrams.Byconnectingwordswitharrows,relationshipsamongsystemvariablesareenteredandrecordedascausalconnections.ThisinformationisusedbytheEquationEditortohelpyouformacompletesimulationmodel.Youcananalyzeyourmodelthroughoutthebuildingprocess,lookingatthecausesandusesofavariable,andalsoattheloopsinvolvingthevariable.Whenyouhavebuiltamodelthatcanbesimulated,Vensimletsyouthoroughlyexplorethebehaviorofthemodel.-VensimUsersGuideVersion5,界面及工具,标题TitleBar,菜单Menu,Toolbar,绘图工具SketchTools,状态条StatusBar,StructuralAnalysisToolsCausesTreecreatesatree-typegraphicalrepresentationshowingthecausesoftheWorkbenchVariable.因果树图UsesTreecreateatree-typegraphicalrepresentationshow