hi, in Matlab i can define a function on a interval(use chebfun)
the code like this :

Code:
v=chebfun('c',[3,5])
 x=sin(v)+cos(v)
 y=sin(v)-cos(v)
 plot(x,y)
then got a figure of x versus y when v is in interval [3,5].

how to do this in sympy??