function [b,a] = f_iirres (F_0,Delta_F,fs)

%F_IIRRES: Design an IIR resonator filter
%
% Usage: [b,a] = f_iirres (F_0,Delta_F,fs)
%
% Inputs: 
%         F_0     = resonant frequency
%         Delta_F = radius of 3dB bandwidth (Delta_F << fs) 
%         fs      = sampling frequency 
% Outputs: 
%          b = 1 by 3 numerator coefficient vector 
%          a = 1 by 3 denominator coefficient vector 
%
% See also: F_IIRNOTCH, F_IIRCOMB, F_IIRINV

% Initialize

fs = f_clip (fs,0,fs);
F_0 = f_clip (F_0,0,fs/2);
Delta_F = f_clip (Delta_F,0,fs/4);

% Find the parameters

r = 1 - (Delta_F*pi/fs);
theta_0 = 2*pi*F_0/fs;
b_0 = abs(exp(j*2*theta_0) - 2*r*cos(theta_0)*exp(j*theta_0) + r^2);
b_0 = b_0/abs(exp(j*2*theta_0)-1);

% Find the coefficient vectors

b = b_0*[1,0,-1];
a = [1,-2*r*cos(theta_0),r^2];