/usr/share/octave/packages/tsa-4.2.7/bispec.m is in octave-tsa 4.2.7-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 | 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.
% $Id: bispec.m 11693 2013-03-04 06:40:14Z schloegl $
% Copyright (C) 1997-2003,2008 by Alois Schloegl <a.schloegl@ieee.org>
%
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% This program 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 General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with this program. If not, see <http://www.gnu.org/licenses/>.
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);
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