heartrate IIR filter

%DESIGNED BY LUZHONGFANG
%DIGITAL SIGNAL PROCESSING OF HEART RATE SIGNAL BY IIR FILTER
clear%清变量
clc%清屏
x=[-4,-2,0,-4,-6,-4,-2,-4,-6,-6,-4,-4,-6,-6,-2,6,12,8,0,-16,-38,-60,-84,-90,-66,-32,-4,-2,-4,8,12,12,10,6,6,6,4,0,0,0,0,0,-2,-4,0,0,0,-2,-2,0,0,-2,-2,-2,-2,0];%original signal
N=length(x);
t=0:1:N-1;
subplot(221);
plot(t,x);%x
title('original signal');
x
%y1
A=0.09036;
B1=1.2686;
C1=-0.7051;
%y1(N);
y1(1)=A*x(1);
y1(2)=A*x(2)+2*A*x(1)+B1*y1(1);
for t1=3:N
y1(t1)=A*x(t1)+2*A*x(t1-1)+A*x(t1-2)+B1*y1(t1-1)+C1*y1(t1-2);%y1
end
subplot(222);
plot(t,y1);
title('original signal->H1(Z)');
y1
%y2
B2=1.0106;
C2=-0.3583;
y2(1)=A*y1(1);
y2(2)=A*y1(2)+2*A*y1(1)+B2*y2(1);
for t1=3:N
y2(t1)=A*y1(t1)+2*A*y1(t1-1)+A*y1(t1-2)+B2*y2(t1-1)+C2*y2(t1-2);%y2
end
subplot(223);
plot(t,y2);
title('original signal->H1(Z)->H2(Z)');
y2
%y3
B3=0.9044;
C3=-0.2155;
y3(1)=A*y2(1);
y3(2)=A*y2(2)+2*A*y2(1)+B3*y3(1);
for t1=3:N
y3(t1)=A*y2(t1)+2*A*y2(t1-1)+A*y2(t1-2)+B3*y3(t1-1)+C3*y3(t1-2);%2
end
subplot(224);
plot(t,y3);
title('original signal->H1(Z)->H2(Z)->H3(Z)');
y3