Another, more general way to fix up the error surface
	• We can leave the error surface alone, but apply the correction to the gradient vector. • We multiply the vector of gradients by the inverse of the curvature matrix. This produces a direction that points straight at the minimum for a quadratic surface. • The curvature matrix has too many terms to be of use in a big network. Maybe we can get some benefit from just using the terms along the leading diagonal (Le Cun).