sigmoid.m

% ============================================================================%
%                 PHAX- initialize weights and do backprop                   %
%                                                                            %
%                      Arash Fayyazi and Mohammad Ansari                     %
%          Low-Power High-Performance Nanosystems Laboratory, Tehran         %
%     SPORT Lab, University of Southern California, Los Angeles, CA 90089    %
%                          http://nanolab.ut.ac.ir/                          %
%                          http://sportlab.usc.edu/                          %
%                                                                            %
%   These models may be freely copied and used for research purposes under   %
%                         the BSD 3-Clause License.                          %
%                                                                            %
%                                                                            %
% Please cite following paper:                                               %
% M. Ansari et al., "PHAX: Physical Characteristics AwareEx-SituTraining     %
% Framework for Inverter-Based Memristive Neuromorphic Circuits," in IEEE    %
% Transactions on Computer-Aided Design of Integrated Circuits and Systems,  %
% vol. 37, no. 8, pp. 1602-1613, Aug. 2018. doi: 10.1109/TCAD.2017.2764070   %
%                                                                            %
%                                                                            %
% ============================================================================%
function g = sigmoid(z,sharp_factor,Vdd)
%SIGMOID Compute sigmoid functoon
%   J = SIGMOID(z) computes the sigmoid of z.
%g =   1.0 ./ (1.0 + exp(-z));
 % g = (1/2) * ((2.0 ./ (1.0 + exp(-z)))-1);
 global cc;
 g = -(Vdd / 2) * tansig(sharp_factor*(z-cc(3)));
end