% FQ2RI Convert frequency/Q pole/zero representation into real
% and imaginary conjugate pairs.
%
% [G,ri]= fq2ri(f0, Q)
%
% M Hewitson 26-01-07
%
% $Id: fq2ri.m,v 1.3 2008/10/24 09:40:19 hewitson Exp $
%
function [G,ri]= fq2ri(f0, Q)
    
  if(nargin==0)
    disp('usage: ri = fq2ri2(f0, Q)')
    return
  elseif(nargin==1 || nargin==2 && isnan(Q))
    ri = -((2*pi*f0));
  elseif(nargin==2 && Q>=0)
    if Q < 0.5
      disp('!!! Q < 0.5! Splitting to two real poles;')
      a = 2*pi*f0/(2*Q)*(1+sqrt(1-4*Q^2));
      b = 2*pi*f0/(2*Q)*(1-sqrt(1-4*Q^2));
      ri = [a b];
    elseif Q == 0.5
      disp('!!! Q = 0.5! Returning one real pole;')
      w0  = 2*pi*f0;
      re  = w0/(2*Q);
      ri  = [re];
    else
      w0  = 2*pi*f0;
      re  = w0/(2*Q);
      im  = w0*sqrt(1-1/(4*Q^2));
      tri = complex(re,im);
      ri  = [tri; conj(tri)];
    end
  end
  
end
% END