logsig.m

Martin T.Hagan等著,戴葵等译,神经网络设计,机械工业出版社,一书的所有例程

function a = logsig(n,b)
%LOGSIG Log sigmoid transfer function.
%	
%	LOGSIG(N)
%	  N - SxQ Matrix of net input (column) vectors.
%	Returns the values of N squashed between 0 and 1.
%	
%	EXAMPLE: n = -10:0.1:10;
%	         a = logsig(n);
%	         plot(n,a)
%	
%	LOGSIG(Z,B) ...Used when Batching.
%	  Z - SxQ Matrix of weighted input (column) vectors.
%	  B - Sx1 Bias (column) vector.
%	Returns the squashed net input values found by adding
%	  B to each column of Z.

% Mark Beale, 1-31-92
% Revised 12-15-93, MB
% Copyright (c) 1992-94 by The MathWorks, Inc.
% $Revision: 1.1 $  $Date: 1994/01/11 16:25:39 $

if nargin < 1, error('Note enough arguments.'); end

if nargin==2
  [nr,nc] = size(n);
  n = n + b*ones(1,nc);
end
a = 1 ./ (1+exp(-n));
i = find(~finite(a));
a(i) = sign(n(i))*0.5 + 0.5;