www.gusucode.com > wavelet工具箱matlab源码程序 > wavelet/wavelet/wlagrang.m
function [P,R] = wlagrang(N) %WLAGRANG "Lagrange a trous" filters computation. % [P,R] = WLAGRANG(N) returns the order N Lagrange filter P. % P has (2N-1) roots located in 1. R contains the other roots % sorted in complex modulus ascending order. % % Possible values for N are: % N = 1, 2, 3, ... % Caution: Instability may occur when N is too large (N > 45). % M. Misiti, Y. Misiti, G. Oppenheim, J.M. Poggi 06-Feb-98. % Last Revision: 14-May-2003. % Copyright 1995-2004 The MathWorks, Inc. lon = 2*N-1; sup = [-N+1:N]; a = zeros(1,N); for k = 1:N nok = sup(sup ~= k); a(k) = prod(0.5-nok)/prod(k-nok); end P = zeros(1,lon); P(1:2:lon) = a; P = [wrev(P),1,P]; if nargout>1 R = roots(P); [s,K] = sort(abs(R+1)); R = R(K(lon+2:2*lon)); [s,K] = sort(abs(R)); R = R(K); end