A simple example
	• We can generate digit images by simulating the physics of drawing. • A pen is controlled by four springs. – The trajectory of the pen is determined by the 4 spring stiffnesses at 17 time steps . • The ink is produced from 60 evenly spaced points along the trajectory: – Use bilinear interpolation to distribute the ink at each point to the 4 closest pixels. – Use time-invariant parameters for  the ink intensity and the width of a convolution kernel. – Then clip intensities above 1.
					We also learn to set the mass, viscosity, and positions of the four endpoints for each image.