www.gusucode.com > signal 工具箱matlab源码程序 > signal/@dfilt/sos.m
%SOS Convert to second-order-sections (for IIR filters only). % Hsos = SOS(Hd) converts IIR discrete-time filter Hd to second-order section % form. Hd can be of class dfilt.df1, dfilt.df1t, dfilt.df2 or % dfilt.df2t. % % SOS(Hd,DIR_FLAG) specifies the ordering of the 2nd order sections. If % DIR_FLAG is equal to 'UP', the first row will contain the poles closest % to the origin, and the last row will contain the poles closest to the % unit circle. If DIR_FLAG is equal to 'DOWN', the sections are ordered % in the opposite direction. The zeros are always paired with the poles % closest to them. DIR_FLAG defaults to 'UP'. % % % Example 1: % [b,a] = butter(8,.5); % Hd = dfilt.df2(b,a); % Hsos = sos(Hd,'up',inf) % % % Example 2: % % It is preferable to design directly in SOS form rather than to % % construct the transfer function and then convert which can % % introduce roundoff error % f = fdesign.lowpass('N,F3db',8,0.5); % Hsos = design(f,'butter','FilterStructure','df1sos'); % Copyright 1988-2010 The MathWorks, Inc. % Help for the p-coded SOS method of DFILT.DF1, DFILT.DF1T, DFILT.DF2 and % DFILT.DF2T classes.