function [d1, d2, d3] = d3tanh(a, y)% DTANH  Calculate three first derivatives of 'tanh'% Copyright (C) 1999-2004 Antti Honkela, Harri Valpola,% and Xavier Giannakopoulos.%% This package comes with ABSOLUTELY NO WARRANTY; for details% see License.txt in the program package.  This is free software,% and you are welcome to redistribute it under certain conditions;% see License.txt for details.if nargin < 2,  y = tanh(a);endif nargout == 1  d1 = 1 - (y .^ 2);else  y2 = y .^ 2;  d1 = 1 - y2;  d2 = -2 * y .* d1;  d3 = 2 * d1 .* (3*y2 - 1);end