Update SFCrowd2020.tex

doc/SFCrowd2020.tex

@@ -89,7 +89,13 @@ \section{About Social Force Model}
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+By simulating many such individuals in collective motion, several scenarios in crowd movement were demonstrated, and one is called the “faster-is-slower” effect. This scenario was observed when a crowd pass a bottleneck doorway, and it shows that increase of desired speed (i.e., $|mathbf{v}_i^0(t)|$) can inversely decrease the collective speed of crowd passing through the doorway.  Another paradoxical phenomenon is called “freezing-by-heating,” and it studies two groups of people moving oppositely in a narrow passageway, and the simulation shows that increasing the fluctuation force in Equation (1) can also cause blocking in the counter-flow of pedestrian crowd.  Other spatio-temporal patterns include herding effect, oscillation of passing directions, lane formation, dynamics at intersections and so forth.  
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+In the past decade, the social-force model has generated considerable research on evacuation modeling (Helbing and Johansson, 2010), and it has been integrated into several egress simulators, such as Fire Dynamics Simulator with Evacuation (Korhonen et. al., 2008, Korhonen, 2017), Pedsim, SimWalk, MassMotion (Oasys, 2018), VisWalk, Maces (Pelechano and Badler, 2006) and Menge.   The model has been partly validated based on data sets from real-world experiments. The method of validation involves comparing the simulation of the model with associated observations drawn from video-based analysis (Johansson, Helbing and Shukla, 2007; Johansson et al., 2008).  
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+A criticism about the model, as mentioned before, is that the anisotropic formula of social force disobeys Newton's 3rd law. If the model does not obey Newton 3rd law, it becomes questionable in field of physics studies.  Another problem about the social force is the dilemma of choosing proper parameters to avoid both overlapping and oscillations of the moving pedestrians (Chraibi, et al., 2011).  Certain scenarios about oscillation of walking behavior are not realistic in the physical world.  From the perspective of physics these problems are difficult to deal with.  However, as mentioned previously, human motion is self-driven and self-adapted, and it is subject to both physical laws and psychological principles.  Psychological study will give a new perspective to understand the model and provide us with a new angle to understand the problems.  This is why we want to bridge the gap between psychological studies and physical explanation about this model.  
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 \section{Social Force and Newton Third Law}
 
 This section provides a psychological perspective to reinterpret the social-force, and the concepts of interpersonal distance, proxemics and stress are critically involved.  Very importantly we introduce a new concept of desired distance in the social force, which is the counterpart of the desired velocity in the self-driving force.  With this new concepts we further discuss whether the model is consistent with Newton 3rd Law.