democ1.m

神经网络学习过程的实例程序

%% Competitive Learning
% Neurons in a competitive layer learn to represent different regions of the
% input space where input vectors occur.
% 
% Copyright 1992-2002 The MathWorks, Inc.
% $Revision: 1.18 $  $Date: 2002/04/14 21:26:38 $

%%
% P is a set of randomly generated but clustered test data points.  Here the
% data points are plotted.
%
% A competitive network will be used to classify these points into natural
% classes.

% Create P.
X = [0 1; 0 1];   % Cluster centers to be in these bounds.
clusters = 8;     % This many clusters.
points = 10;      % Number of points in each cluster.
std_dev = 0.05;   % Standard deviation of each cluster.
P = nngenc(X,clusters,points,std_dev);

% Plot P.
plot(P(1,:),P(2,:),'+r');
title('Input Vectors');
xlabel('p(1)');
ylabel('p(2)');

%%
% Here NEWC takes three input arguments, an Rx2 matrix of min and max values for
% R input elements, the number of neurons, and the learning rate.
% 
% We can plot the weight vectors to see their initial attempt at classification.
% The weight vectors (o's) will be trained so that they occur centered in
% clusters of input vectors (+'s).

net = newc([0 1;0 1],8,.1);
w = net.IW{1};
plot(P(1,:),P(2,:),'+r');
hold on;
circles = plot(w(:,1),w(:,2),'ob');


%%
% Set the number of epochs to train before stopping and train this competive
% layer (may take several seconds).
% 
% Plot the updated layer weights on the same graph.

net.trainParam.epochs = 7;
net = train(net,P);
w = net.IW{1};
delete(circles);
plot(w(:,1),w(:,2),'ob');


%%
% Now we use the competitive layer as a classifier, where each neuron
% corresponds to a different category.  Here we present the input vector [0;
% 0.2].
% 
% The output, a, indicates which neuron is responding, and thereby which class
% the input belongs. Note that SIM returns outputs in sparse matrix form for
% competitive layers.

p = [0; 0.2];
a = sim(net,p)