crossentropy_snn.m

神经网络的工具箱, 神经网络的工具箱,

function f = crossentropy_snn(a, t)
%CROSSENTROPY_SNN Cross entropy error.
%
%  Syntax
%
%   f = crossentropy_snn(y, t)
%
%     y - output
%     t - target
%     f - cross entropy error
%

if isstr(a)
   switch lower(a)
     case 'deriv',
	  f = 'dcrossentropy_snn';
     case '2deriv',
          f = 'd2crossentropy_snn';
     case 'inv',
          f = 'invcrossentropy_snn';
     otherwise,
	  error('Unrecognized code.')
   end
   return
end

TINY = 1e-8;

a(find(a>=1.0)) = 1.0 - TINY;
a(find(a<=-1.0)) = -1.0 + TINY;

f = zeros(size(a));
indices = find(t==1);
f(indices) = (1+a(indices)).^(-2);
indices = find(t==-1);
f(indices) = (1-a(indices)).^(-2);
indices = find((t~=1) & (t~=-1));
f(indices) = 0.5 * ( (1+t(indices)).*log((1+t(indices))./(1+a(indices))) ...
                   + (1-t(indices)).*log((1-t(indices))./(1-a(indices))) );