 Usage:  nnrtrain (ntr, data, weights)  
 
 Input:

  ntr                    scalar number of observations 
                         
  data                   n x (p+q) matrix of input and output data 
                         
  weights                n x 1 vector of weights for each observation 
                         
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(C) MD*TECH Method and Data Technologies, 17.8.2000
