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Vensim
Download:
http://www.vensim.com/cgibin/download.exe
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Menu dan Toolbar
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MENU File : Open Model, Save, Print, dll. Ed it : copy and paste, search, dll View : manipulating the sketch of the model and for
viewing a model Layou t : manipulate the position and size of elements
in the sketch. M od e l : Simulation Control and the Time Bounds
dialogs, the model checking features, and importing and
exporting datasets. Tools : sets Vensim's global options and allows you tomanipulate Analysis tools
W in d o w s : to switch among different open windows. H e lp : provides access to the on-line help system.
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Toolbar
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Sketch Tools
Lock sketch is locked.
Move/Size move, sizes and selects sketch objects: variables, arrows, etc.
Variable creates variables ( Constants , Auxiliaries and Data).
Box Variable create variables with a box shape (used for Levels or Stocks).
Arrow creates straight or curved arrows.
Rate creates Rate (or flow) construct
Model Variable adds an existing model variable
Shadow Variable adds as a shadow variable
Merge merges two variables into a single variable, etc
Input Output Object adds input Sliders and output graphs and tables to the sketch.
Sketch Comment adds comments and pictures to the sketch.
Unhide Wand unhides (makes visible) variables in a sketch view.
Hide Wand hides variables in a sketch view.
Delete deletes structure, variables in the model, and comments in a sketch.
Equations creates and edits model equations using the Equation Editor.
Reference Modes use to draw and edit reference models.
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Analysis Tool Output
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Control Panel
Variable allows you to choose a variable in your model and select it as the Workbench
Variable.
Time Axis allows you to change or focus the period of time over which Analysis tools
operate.
Scaling enables you to change the scales of output graphs.
Datasets allows you to manipulate the stored datasets (runs).
Graphs brings up the Custom Graph Control.
Placeholders is a control that sets Placeholder Values
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Example of Vensim
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Level
Rate
Auxiliary
Source/Sink
Constant
Flow arc
Cause-and-effect arc
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Level: Stock, accumulation, or state variableA quantity that accumulates over time
Change its value by accumulating or integratingrates
Change continuously over time even when therates are changing discontinuously
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Rate/ Flow: Flow, activity, movement
Change the values of levels
The value of a rate is
Not dependent on previous values of that rate
But dependent on the levels in a system along with
exogenous influences
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Auxiliary: Arise when the formulation of a levels influence on
a rate involves one or more intermediate
calculations Often useful in formulating complex rate equations
Used for ease of communication and clarity
Value changes immediately in response to changesin levels or exogenous influences
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Source and Sink: Source represents systems of levels and rates
outside the boundary of the model
Sink is where flows terminate outside the system
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Example 1(Population and birth)
+
+
Births Population
Births
Population
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Example 2(Children and adults)
Births Children Children maturing Adults
+ + +
+-
+
-
Births
children
Childrenmaturing
Adults
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average lifetime = 8 Units: Year
birth rate = 0.125 Units: fraction/Year
births = Population * birth rate Units: rabbit/Year
deaths = Population / average lifetime
Units: rabbit/Year
Population = INTEG(births - deaths,1000) Units: rabbit
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From Causal Loop DiagramTo Simulat ion Models 1
R
L
Equations
dL/dt = k1*R(t)
R(t) = k2*L(t)
dL/dt = k1*k2*L(t)
Flow Graph
Block Model
L L
k1*k2
Causal Graph
+
+
R L
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From Causal Loop DiagramTo Simulat ion Models 2R1
L
Equations
dL/dt = R1 R2
R2 = k2*L
R1 = k1
dL/dt = k1 - k2*L
Flow Graph
Block Model
R2
L1 L1k2
- k1
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From Causal Loop Diagram
To Simulat ion Models 3
Equations
dL1/dt = R1 R2
dL2/dt = R2 R3
R1 = k1
R2 = K2 * L1
R3 = K3 * L2
dL1/dt = k1 k2*L1
dL2/dt = k2*L1 K3*L2
R1
L1
Flow Graph
R2
L2
R3
L1 L1
k2
-
-
k1
L2 L2
Block Model
k3
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Building construction
Problem statementFixed area of available land for constructionNew buildings are constructed while old buildings are demolishedPrimary state variable will be the total number of buildings over time
Causal Graph
Industrialbuildings
DemolitionConstruction
Fraction of
land occupied
Construction
fraction Averagelifetime
for buildings
Average area
per building
Land available forIndustrial buildings
+
+
+
+
+
+ -
-
-
-
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Simulation models
Industrial
Buildings (B)
Construction (C) Demolition (D)
Construction
fraction
(CF) Fraction ofland occupied
(FLO)Land available forindustrial buildings(LA)
Average areaper building(AA)
Average lifetimefor buildings (AL)
Equations
dBl/dt = Cr Dr
Cr = f1(CF, Bl)
Dr = f2(AL,Bl)
CF = f3(FLO)
FLO = f4(LA,AA,Bl)
Flow Graph
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