It's a way of living to view our world as a big working model, controlable and well in human's recognition; but it's not true.
The goal of doing simulations -- of the natural systems -- lies in several lines: a better understanding of how they currently work; a help directing to what we actually wish they be; and for future mysterious discoveries that might enhance up to an overall knowledge level.

However, I feel it not an easy job, since enormous factors are concerned. Basicly we can name them into three questions:

First, is our attempting model reflexing well to the reality? In a good situation, these two conceptually coincide and what we need is to eliminate mankind errors, and try to reach most precision; but to a worse case, the model might be totally wrong. This is a question of the nature of model. Second, what form of model it will be? How much we've already know and how much not, and in what manner to represent the two parts respectively? This I call as the physics of model. Third, Are there ways to examine our model's properties such as correctness, robustness, stability? Is there a feedback judgement from the systems we examine and a modification on the model? This can be said the elaboration of model.

From a procedural view, simulation can be separated into system modeling and system identification, two interleaving processes during this work. Many topics are involved and people diver greatly.
--  Uncertainty: incasual phenomenon of casualty
Uncertainty is an inevitable part of the assertion of knowledge. In maths, there're several disciplines studying on it, such as probability (Bayesian mass distribution), epistemic knowledge (Dempster-Shafer belief functions, or, sets of possibilities), fuzzy logic (logic of patial truth), game theory, etc. In physics there exists the famous (Heisenberg) uncertainty principle that leads to the basics of quantum mechanics.

On simulation, however, the focus is how to simulate the phenomenon which we can only know from experimental data by a mathematical model to a certain precision. The method for solving uncertainty that I'm interested (or say, my supervisor indicated, :-)) is called interval analysis or known as set membership estimation.
--  Model physics: different axes of classification
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--  Elaboration on models: procedure and principles
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My specific topic of internship is "parametric identification by set membership method"; in more detail, looking into a two-axed domain -- simulation and inversion, I'm going to find a numerical Hermit-Obreschoff expansion for the implicit ordinary differential equation model for thermodynamic diffusion. I'm facing the faisability of this algorithm and also size problem.

I'm currently studying system identification, numercial resolution to ordinary differential equations, and interval analysis. (These three might form a "why-what-how" structure.) Under the supervision of Mr. Nacim Ramdani. Partial technical report is here.
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