discontinuos function



On Thu, 2010-03-18 at 14:11 -0300, Alexandre Campos wrote:
> how can I express  and plot a  function (singular function)  like:
> 
> f(x) = <x-a> 
> 
> where
> 
> <x-a> =     0      --------------if x<a
>                  (x-a) --------------if x>=0 

Do you mean something like this?:
(%i1) f(a,x):= if x > a then x-a else 0$
(%i2) plot2d(f(2,x), [x,-4,4], [y,-1,5])$

Regards,
Jaime