Analog IIR filter to Digital IIR Filter - Backward Difference

This Program is used To convert analog filter into digital filter using
Backward Difference  method

//Program To convert analog filter into digital filter using
//mapping = (z-(z^-1))/T - Backward Difference  
clear all;
clc;
close;
s = poly(0,'s');
H = 1/((s+0.1)^2+9)
T =1;//Sampling period T = 1 Second
z = poly(0,'z');
Hz = horner(H,(1/T)*(z-(z^-1)))