232 Chapter 6 Neural Networks
number of units. However, there is no unified theory yet as to how many hid-
den units are needed to approximate any given function. Unfortunately, using
two hidden layers increases the problem of local minima, and it is important
to use random initializations or other methods for global optimization. Local
minima arising with two hidden layers can have extreme spikes even when
the number of weights is much smaller than the number of training cases.
6.4.2 Number of Hidden Nodes
There is no way of determining good network architecture just from the
number of inputs and outputs. This mainly depends on the number of
training cases, the amount of noise, and the complexity of the function the
network ...