Daniel@0: function [y, l] = knnfwd(net, x)
Daniel@0: %KNNFWD	Forward propagation through a K-nearest-neighbour classifier.
Daniel@0: %
Daniel@0: %	Description
Daniel@0: %	[Y, L] = KNNFWD(NET, X) takes a matrix X of input vectors (one vector
Daniel@0: %	per row)   and uses the K-nearest-neighbour rule on the training data
Daniel@0: %	contained in NET to  produce  a matrix Y of outputs and a matrix L of
Daniel@0: %	classification labels. The nearest neighbours are determined using
Daniel@0: %	Euclidean distance. The IJth entry of Y counts the number of
Daniel@0: %	occurrences that an example from class J is among the K closest
Daniel@0: %	training examples to example I from X. The matrix L contains the
Daniel@0: %	predicted class labels as an index 1..N, not as 1-of-N coding.
Daniel@0: %
Daniel@0: %	See also
Daniel@0: %	KMEANS, KNN
Daniel@0: %
Daniel@0: 
Daniel@0: %	Copyright (c) Ian T Nabney (1996-2001)
Daniel@0: 
Daniel@0: 
Daniel@0: errstring = consist(net, 'knn', x);
Daniel@0: if ~isempty(errstring)
Daniel@0:   error(errstring);
Daniel@0: end
Daniel@0: 
Daniel@0: ntest = size(x, 1);		              % Number of input vectors.
Daniel@0: nclass = size(net.tr_targets, 2);		% Number of classes.
Daniel@0: 
Daniel@0: % Compute matrix of squared distances between input vectors from the training 
Daniel@0: % and test sets.  The matrix distsq has dimensions (ntrain, ntest).
Daniel@0: 
Daniel@0: distsq = dist2(net.tr_in, x);
Daniel@0: 
Daniel@0: % Now sort the distances. This generates a matrix kind of the same 
Daniel@0: % dimensions as distsq, in which each column gives the indices of the
Daniel@0: % elements in the corresponding column of distsq in ascending order.
Daniel@0: 
Daniel@0: [vals, kind] = sort(distsq);
Daniel@0: y = zeros(ntest, nclass);
Daniel@0: 
Daniel@0: for k=1:net.k
Daniel@0:   % We now look at the predictions made by the Kth nearest neighbours alone,
Daniel@0:   % and represent this as a 1-of-N coded matrix, and then accumulate the 
Daniel@0:   % predictions so far.
Daniel@0: 
Daniel@0:   y = y + net.tr_targets(kind(k,:),:);
Daniel@0: 
Daniel@0: end
Daniel@0: 
Daniel@0: if nargout == 2
Daniel@0:   % Convert this set of outputs to labels, randomly breaking ties
Daniel@0:   [temp, l] = max((y + 0.1*rand(size(y))), [], 2);
Daniel@0: end