Fig. 4
From: A model for inference of emotional state based on facial expressions
An emotional curve. In this example the system detected an expression related to sadness, thus the particle has a \(\overrightarrow{V}_\mathrm{sad}\) component. The sliding velocity is represented as \(\overrightarrow{V}_\mathrm{slide}\) and it is proportional to the curve steepness, that is, tending to a stable point, normally neutral emotion