%SIGM Sigmoid map
%
% W = W*SIGM(SCALE)
%
% B = SIGM(A,SCALE)
% B = A*SIGM([],SCALE)
% B = A*SIGM(SCALE)
%
% INPUT
% A Dataset (optional)
% SCALE Scaling parameter (optional, default: 1)
%
% OUTPUT
% W Sigmoid mapping, or
% B Dataset A mapped by sigmoid mapping
%
% DESCRIPTION
% Sigmoidal transformation, useful to transform a map to classifier,
% producing posterior probability estimates. The parameter SCALE scales the
% data first (A/SCALE), before the transformation. Default: SCALE = 1, i.e.
% no scaling.
%
% SEE ALSO (<a href="http://37steps.com/prtools">PRTools Guide</a>)
% DATASETS, MAPPINGS, CLASSC
% Copyright: R.P.W. Duin, duin@ph.tn.tudelft.nl
% Faculty of Applied Sciences, Delft University of Technology
% P.O. Box 5046, 2600 GA Delft, The Netherlands
function out = sigm (varargin)
argin = shiftargin(varargin,'scalar');
argin = setdefaults(argin,[],1);
if mapping_task(argin,'definition')
out = define_mapping(argin,'fixed','Sigmoidal Mapping');
else % Evaluate
[a,scale] = deal(argin{:});
out = 1./(1+exp(-a/scale));
end
return