LPF and HPF from APF

i came across a concept that says we can design LPH and HPF from APF when the transfer function of the two APFs given as

A0=1;

A1=-a+z^-1/1-az^-1;

LPF=A0+A1;HPF=A0-A1;

i tried to implement this in matlab but i did not get the desired frequency response..kindly help me with the matlab code for the same..

[pavan sunder]

bro i had shared you the derivation did u see that ?? i dunno its got deleted

[Walter Roberson]

Please show your attempt, and please describe the frequency response that you desire.

[pavan sunder]

i want a low pass response..there is a concept says we can design LPH or HPF from two APF when the transfer function of the two APFs given as

A0=1;

A1=-a+z^-1/1-az^-1;

LPF=A0+A1;

HPF=A0-A1;

though i got the response, its not varying when i change a..kindly help me with a matlab code..

here is the response is got for my code.