more RBF refs

[Eric Hartman]

Here are a couple more RBF refs:

    Hartman, Keeler & Kowalski 
      Layered Neural Networks With Gaussian Hidden Units 
      as Universal Approximators
      Neural Computation, 2 (2), 210-215 (1990)

    Hartman & Keeler
      Semi-local Units for Prediction
      IJCNN-91-Seattle, II-561-566 

The latter describes some limitations of RBFs and a new
activation function that is less localized than an RBF
but more localized than a sigmoid.  The function is based
on gaussians;  backpropagation networks using these basis 
functions learn the Mackey-Glass time series nearly as fast 
as the standard RBF network training algorithm.  The full 
paper will appear in Neural Computation.

Eric Hartman and Jim Keeler