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At the other extreme quantification of a outcome

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Unformatted text preview: • • An abstraction of reality designed to answer specific questions about the real world An imitation, analogue, or representation of a real world process or structure; or A conceptual, mathematical, or physical tool to assist a decision maker. Together, these definitions are broad enough to encompass physical engineering models used in the verification of a system design, as well as schematic models like a functional flow block diagram and mathematical (i.e., quantitative) models used in the trade study process. This section focuses on the last. The main reason for using mathematical models in trade studies is to provide estimates of system effectiveness, performance or technical attributes, and cost from a set of known or estimable quantities. Typically, a collection of separate models is needed to provide all of these outcome variables. The heart of any mathematical model is a set of meaningful quantitative relationships among its inputs and outputs. These relationships can be as simple as adding up constituent quantities to obtain a total, or as complex as a set of differential equations describing the trajectory of a spacecraft in a gravitational field. Ideally, the relationships express causality, not just correlation. Types of Models. There are a number of ways mathematical models can be usefully categorized. One way is according to its purpose in the trade study process—that is, what system issue and what level of detail the model addresses, and with which outcome variable or variables the model primarily deals. Other commonly used ways of categorizing mathematical models focus on specific model attributes such as whether a model is: • • • Static or dynamic Deterministic or probabilistic stochastic) Descriptive or optimizing. (also called These terms allow model builders and model users to enter into a dialogue with each other about the type of model used in a particular analysis or trade study. No hierarchy is implied in the above list; none of the...
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