/usr/share/octave/site/m/vlfeat/toolbox/special/vl_sigmoid.m is in octave-vlfeat 0.9.17+dfsg0-6+b1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | function y = vl_sigmoid(x)
% VL_SIGMOID Sigmoid function
% Y = VL_SIGMOID(X) returns
%
% Y = 1 ./ (1 + EXP(X)) ;
%
% Remark::
% Useful properties of the sigmoid function are:
%
% - 1 - VL_SIGMOID(X) = VL_SIGMOID(-X)
% - Centered sigmoid: 2 * VL_SIGMOID(X) - 1 ;
% - VL_SIGMOID(X) = (EXP(X/2) - EXP(X/2)) / (EXP(X/2) + EXP(X/2))
%
% See also: VL_DSIGMOID(), VL_HELP().
% Copyright (C) 2007-12 Andrea Vedaldi and Brian Fulkerson.
% All rights reserved.
%
% This file is part of the VLFeat library and is made available under
% the terms of the BSD license (see the COPYING file).
y = 1 ./ (1 + exp(-x)) ;
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