s-parameter conversion

hi noorm,
check this link

http://www.rfcafe.com/references/electrical/s-h-y-z.htm

Refer to text books as "Microwave Engineering" by David Pozar.

Also, many softwares have these conversion functions, you even do not need to know about the background theory but be careful about the Characteristic Impedance set up.
for example, ADS, Matlab.

i mean i need matlab code for these conversions

you can write the expressions in the above link in MATLAB.

good luck,

if you use the ADS, you can check the Y parameter, and you can get the Y Parameter dircetly.
and I think you can also transfer it easily in other software.