Optimal Brain Surgeon (OBS) is about pruning neural networks to minimize the amount of parameters, training time and overfitting. It is very similar to [Optimal Brain Damage](http://www.shortscience.org/paper?bibtexKey=conf/nips/CunDS89#martinthoma), but claims to choose better weights. However, it does require to compute the inverse hessian. The hessian matrix of a neural network is a $n \times n$ matrix, where $n$ is the number of parameters of the network. Typically, $n > 10^6$. This makes the approach unusable.