the system engineer may try to deal with that

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Unformatted text preview: above dichotomous categorizations stands above the others. NASA Systems Engineering Handbook Systems Analysis and Modeling Issues Another taxonomy can be based on the degree of analytic tractability. At one extreme on this scale, an "analytic" model allows a closed-form solution for a outcome variable of interest as a function of the model inputs. At the other extreme, quantification of a outcome variable of interest is at best ordinal, while in the middle are many forms of mathematical simulation models. Mathematical simulations are a particularly useful type of model in trade studies. These kinds of models have been successfully used in dealing quantitatively with large complex systems problems in manufacturing, transportation, and logistics. Simulation models are used for these problems because it is not possible to "solve" the system's equations analytically to obtain a closed-form solution, yet it is relatively easy to obtain the desired results (usually the system's behavior under different assumptions) using the sheer computational power of current computers. Linear, nonlinear, integer and dynamic program ming models are another important class of models in trade studies because they can optimize an objective function representing an important outcome variable (for example, system effectiveness) for a whole class of implied alternatives. Their power is best applied in situations where the system's objective function and constraints are well understood, and these constraints can be written as a set of equalities and inequalities. Pitfalls in Using Models. Models always embody assumptions about the real world they purport to represent, and they always leave something out. Moreover, they are usually capable of producing highly accurate results only when they are addressing rigorously quantifiable questions in which the "physics" is well understood as, for example, a load dynamics analysis or a circuit analysis. In dealing with system issues at the top level, however, this is seldom the case. There is often a significant difference between the substantive system cost-ef...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.

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