Technology for the United States Navy and Marine Corps, 2000-2035: Becoming a 21st-Century Force Volume 9: Modeling and Simulation (1997) / Chapter Skim
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Appendix E
Appendix E
Pages 184-203
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From page 184... ...
and the related subject of integrated families of models.) These have to do with changing resolution within a single model or connecting two or more models and the key issue doing so in a substantively valid way.
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From page 185... ...
Further, as computing power has increased, some workers have become interested in doing analysis with models that normally operate at one level of resolution, but occasionally call higher-resolution subroutines. There are many reasons for operating at multiple levels in an advanced distributed simulation (ADS)
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From page 186... ...
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From page 187... ...
They care deeply what goes on at higher levels of detail, but they can only check on such matters by exception. Instead, they must depend on doctrinal planning factors, aggregate models, and judgment with occasional high-resolution "calibrations." It is worth noting here that most analyses and exercises depend on being able to treat key phenomena in relatively higher detail than other, less-central phenomena.
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From page 188... ...
How Multiple Resolutions Arise in Simulations Multiple resolutions are needed even within individual simulations, especially in the distributed simulation environments central to the future of DOD's M&S. Some examples of why follow.
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From page 189... ...
If one object changes resolution several times in a row, how can we ensure that the sequence of detailed views represents a coherence sequence? For example, as a battalion deaggregates, reaggregates, and deaggregates again, how can we make sure that the subordinate platoons (or even subordinate tanks)
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From page 190... ...
The difficulties in discussing variable resolution or multi-level resolution begin with the word "resolution," since resolution is multifaceted as Figure E.1 suggests. To make matters worse, in comparing two typical military models, one often discovers that the first model has higher resolution in some respects and lower resolution in others.
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From page 191... ...
Figure E.2 depicts the issues graphically. If G and g are high-resolution and low-resolution models, which operate on initial states to generate subsequent states, then the first question of consistency is whether one can start at the top left corner with an initial detailed state and get the same aggregate state by aggregating the initial state and applying the aggregate model (down and right)
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From page 192... ...
Now to establish that this correspondence is a homomorphism requires that whenever S' makes a transition, such as from state b to state c, then S actually makes the sequence of transitions involving corresponding states B and C Some points to notice in this definition are as follows: · The situation where S has many more states than S' occurs in two major contexts: in multi-resolution modeling when S is a high-resolution model and S' is a consistent (i.e., homomorphic)
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From page 193... ...
· A second important place where the concept of experimentalframe helps bring clarity is in the relationship of the complete state of a model and its observable output. An experimental frame specifies the variables in which we are interested for some particular exercise.
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From page 194... ...
, but rather as suggested to us by John Doyle to create "good seams," so that moving across levels of resolution maintains a clear and consistent sense of the system. Integration of models has always been desirable, but analysts working in a single small organization have often been able to work around problems by studying the various models in detail and developing "good-enough" procedures.
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From page 195... ...
Similarly, much of our best knowledge of military operations comes from aggregate-level observations and is expressed in the concepts of aggregate models. The commonly held notion that the best information resides only at high resolution is wrong.
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From page 196... ...
Remarkably, modelers often display more hubris than humility in this regard. "Designing on the fly" at the computer terminal, they do violence to the underlying phenomena as they assume aggregate relationships that ignore complications and assume, implicitly or explicitly, circumstances such as uniform distributions, independent events, and constant remixing.
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From page 197... ...
This would be possible if the probability distribution of leakage rates assumed at Level 2 was generated from Level 3 analysis averaged appropriately over all the relevant operational circumstances. In some cases, it might be adequate at Level 2 to use a "best estimate leakage" and an uncertainty range, without the embellishment of a probability distribution.
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From page 198... ...
The conclusion here is that we should not assume that a given set of hierarchical relationships would always be "right." Analysts understand this viscerally, but simulation modelers sometimes tend to think of their preferred representations as being uniquely correct. LOOKING AHEAD: NEXT STEPS IN UNDERSTANDING HOW TO DO VARIABLE RESOLUTION DESIGNS Past militarily relevant work has contributed to a better understanding of the conditions under which various idealized aggregate models are or are not consistent with higher-resolution idealized depictions.
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From page 199... ...
Such developments would be quite valuable in efforts to build variable-resolution or multi-level resolution models.8 Thus, the efforts of OSD's Defense Modeling and Simulation Office to encourage common models of the mission space (CMMS) should be supported.
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From page 200... ...
Finding the appropriate scales and ways to exploit them will not necessarily be easy because warfare operations have become quite complex as maneuver of forces has begun to give way to maneuver of fire, as lethality has increased, and as a relatively small number of C4ISR systems have come to play an increasingly critical role. It is also plausible that aggregate models will sometimes not be as useful as in earlier days because the decisive events may be fewer in number and more highly correlated.
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From page 201... ...
Or should one instead run a large number of the high-resolution cases using different input parameter values, and then somehow average the results statistically? If so, what statistical approach would be suitable for the problem at hand?
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From page 202... ...
Aggregate-level data may have important implications for high-resolution models (e.g., the implication that unmodeled frictions slow processes up) , and vice versa (e.g., a serious mismatch between the effective shooting ranges of the adversaries may mean that aggregate models based on Lanchester equations or anything remotely comparable will fail catastrophically under some circumstances, as happened in Desert Storm in n art due to Door Practices bv the Iraoi ground forces (Biddle, 1996~.
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From page 203... ...
features a review of recent work on model abstraction and its latest developments. CONCLUSIONS The next generation of military models needs to be designed so as to produce integrated families that cross levels of resolution.
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