www.gusucode.com > 时间序列分析工具箱 - tsa源码程序 > tsa/bispec.m
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);