crosslogistic_snn.m

神经网络的工具箱, 神经网络的工具箱,

function f = crosslogistic_snn(a, t)
%CROSSLOGISTIC_SNN Cross logistic error.
%
%  Syntax
%
%   f = crosslogistic_snn(y, t)
%
%     y - output
%     t - target
%     f - cross entropy error
%

if isstr(a)
   switch lower(a)
     case 'deriv',
	  f = 'dcrosslogistic_snn';
     case '2deriv',
          f = 'd2crosslogistic_snn';
     case 'inv',
          f = 'invcrosslogistic_snn';
     otherwise,
	  error('Unrecognized code.')
   end
   return
end

TINY = 1e-8;

a(find(a>=1.0)) = 1.0 - TINY;
a(find(a<=0.0)) = TINY;

f = zeros(size(a));
indices = find(t);
f(indices) = -log(1 - a(indices));
indices = find(t==1.0);
f(indices) = -log(a(indices));
indices = find ((t ~= 0) & (t ~= 1.0));
f(indices) = t(indices).*log(t(indices)./a(indices)) + ...
             (1-t(indices)).*log((1-t(indices))./(1-a(indices)));