To cover most cases, you could do:
cd ~/Desktop
if you're running linux or Mac, Or:
[a,b] = system('echo %UserProfile%\Desktop')
cd(b)
on windows. I'm on a linux machine, so I haven't tested the windows solution. You may need to tweak it. If your machine is set up in some non-standard way, or you're using some other OS, then this may not apply.
