function [BISPEC,BIACF,ACF] = bispec(Z,N);% Calculates Bispectrum % [BISPEC] = bispec(Z,N);%% Input:	Z    Signal%		N  # of coefficients% Output:	BiACF  bi-autocorrelation function = 3rd order cumulant%		BISPEC Bi-spectrum %% Reference(s):% C.L. Nikias and A.P. Petropulu "Higher-Order Spectra Analysis" Prentice Hall, 1993.% M.B. Priestley, "Non-linear and Non-stationary Time series Analysis", Academic Press, London, 1988.%	$Revision: 1.8 $%	$Id: bispec.m,v 1.8 2005/05/31 14:30:57 qspencer Exp $%	Copyright (C) 1997-2003 by Alois Schloegl <a.schloegl@ieee.org>% This library is free software; you can redistribute it and/or% modify it under the terms of the GNU Library General Public% License as published by the Free Software Foundation; either% version 2 of the License, or (at your option) any later version.% % This library is distributed in the hope that it will be useful,% but WITHOUT ANY WARRANTY; without even the implied warranty of% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU% Library General Public License for more details.%% You should have received a copy of the GNU Library General Public% License along with this library; if not, write to the% Free Software Foundation, Inc., 59 Temple Place - Suite 330,% Boston, MA  02111-1307, USA.P=N+1;ACF=zeros(1,N+1);BIACF=zeros(2*N+1,2*N+1);Z=Z(:);M=size(Z,1);M1=sum(Z)/M;Z=Z-M1*ones(size(Z));for K=0:N, 	jc2=Z(1:M-K).*Z(1+K:M);	ACF(K+1)=sum(jc2)/M;	for L = K:N,		jc3 = sum(jc2(1:M-L).*Z(1+L:M))/M;		BIACF(K+P,  L+P)  =jc3;		BIACF(L+P,  K+P)  =jc3;		BIACF(L-K+P, -K+P)=jc3;		BIACF(-K+P, L-K+P)=jc3;		BIACF(K-L+P, -L+P)=jc3;		BIACF(-L+P, K-L+P)=jc3;	end;end;BISPEC=fft2(BIACF,128,128);