For (-1,+1) you can use something like the following.
F for Flip
F= 2*(t-.5)
t=0 , F=-1
t=.5 , F=0
t=1 , F=1
For Variable Section sweeps you follow the same techniques except t has a [/b]rajpar[/b] appended to it any t will be trajpar in the relation.
Trajpar is 0 at start of sweep and 1 at the other end just like T in curve by Equation.
Michael