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function [z,p,k] = sos2zp (sos, g)
//This function converts series second-order sections to zeros, poles, and gains (pole residues).
//Calling Sequence
//z = sos2zp (sos)
//z = sos2zp (sos, g)
//[z, p] = sos2zp (...)
//[z, p, k] = sos2zp (...)
//Parameters
//sos: matrix of real or complex numbers
//g: real or complex value, default value is 1
//z: column vector
//p: column vector
//Description
//This function converts series second-order sections to zeros, poles, and gains (pole residues).
//The input is the sos matrix and the second parameter is the overall gain, default value of which is 1.
//The outputs are z, p, k. z and p are column vectors containing zeros and poles respectively, and k is the overall gain.
//Examples
//[a,b,c]=sos2zp([1,2,3,4,5,6])
//a =
// -1.0000 + 1.4142i
// -1.0000 - 1.4142i
//b =
// -0.6250 + 1.0533i
// -0.6250 - 1.0533i
//c = 1
if(argn(2)<1 | argn(2)>2)
error("Wrong number of input arguments.")
end
if argn(2)==1 then
g=1;
end
gns = sos(:,1);
k = prod(gns)*g;
if k==0 then
error('one or more section gains is zero');
end
sos(:,1:3) = sos(:,1:3)./ [gns gns gns];
[N,m] = size(sos);
if m~=6 then
error('sos matrix should be N by 6');
end
z = zeros(2*N,1);
p = zeros(2*N,1);
for i=1:N
ndx = [2*i-1:2*i];
zi = roots(sos(i,1:3));
z(ndx) = zi;
pi = roots(sos(i,4:6));
p(ndx) = pi;
end
endfunction
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