# page_69 - R is a rate the amount of something that flows in...

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< previous page page_69 next page > Page 69 Figure 4.4 System dynamics diagrammatic representation of stock level, 1 Figure 4.5 System dynamics diagrammatic representation of stock level, 2

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the addition of an auxiliary (symbolised by a circle), a "source" or "sink" (symbolised by a cloud) and a constant (a small flying saucer). The whole diagram reads: there is a stock level which is increased by supply of manufacturing output and decreased by delivery to customers. If the level begins to decrease then this indicates an increase in demand and hence should lead to an increase in manufacturing rate. This allows the stock level to return to a desired level. The logic of all this can be summarised as follows (see Figure 4.6).
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Unformatted text preview: R is a rate, the amount of something that flows in a given time period (per unit time); L is a level, the accumulation of rates added to an initial condition; A is an auxiliary variable. Levels and rates are necessary to describe a situation. Auxiliaries are used to break down rate equations into manageable parts, to convert flows from one type to another and to provide information to change/control rates, which is particularly useful when we come to writing sets of equations from the SD diagram. Rules of this logic, captured in Figure 4.6, are as follows. A level in a loop can only be preceded by a rate. < previous page page_69 next page >...
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## This note was uploaded on 04/21/2011 for the course MGT 03 taught by Professor Kasra during the Spring '11 term at Tanta University.

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page_69 - R is a rate the amount of something that flows in...

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