and forward
propagates the inputs through the network to generate a structure
<CODE>mixparams</CODE> which contains the parameters of several mixture models.  
Each row of <CODE>x</CODE> represents
one input vector and the corresponding row of the matrices in <CODE>mixparams</CODE> 
represents the parameters of a mixture model for the conditional probability
of target vectors given the input vector.  This is not represented as an array
of <CODE>gmm</CODE> structures to improve the efficiency of MDN t