waiting lines, an explicit line build-ip as opposed to a pile-up implied by a resevoir
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waiting lines, an explicit line build-ip as opposed to a pile-up implied by a resevoir. in the STELLA software, they are used in conjunction with a conveyor to represent batches of material waiting to enter a process or activity
a way to designate the value of a variable to change linearly over time
definition of the present, instantaneous flow to and from a level in a system. rates represent activity, while levels represent the state to which the system has been brought by the activity. Rates are determined by the levels of a system according to rules defined by the decision functions. in turn, rates cause levels to change
loops that occurs when an action causes change that accelerates that action, reinforcing the effect of the original action. associated with positive feedback
the type of stock that is analogous to a tub with water flowing in a draining out. in many ways it is the simplest of stocks. when something flows into a tub, it is mixed into any "stuff" that is already in the tub so that it cannot be distinguished from earlier or later inflows
analysis used to determine how "sensitive" a model is to changes in specific parameters, or policies, or structures. if the behavior of a model changes drastically, that suggests a critically important factor, or high sensitivity. conversely, if a large change results in little change in behavior, that factor is not likely to be central to the dynamics in question, that is, it shows low sensitivity
a system behavior where an intervener acts to improve a system and the effort fails because the system lacks incentive to continue its own effort to take the action
conducting dynamic experiements on a model instead of on the real system
filtering out the superimposed short-term fluctuations in order to detect underlying, significant changes in data. there is formal (numerical processing of data into averages) and intuitive smoothing
the amount of time elapsed between successive computer calculations of flows accumulating into stocks. also known as computation interval or DT (for Delta Time). It is measured in units of time and must be short enough so that its value does not affect the computed results, but also long enough to avoid unnecessary waste of computation time
