order of points in spline

Huh?

Prevent spline from using (x[n],y[n]) as the coordinates of the n^{th} data point?

Why on earth would you want to do that?

Maybe I did not explain myself correctly.

My first three points have x:  262, 275, 264

I want the spline to go from point 1 (x=262) to point 2 (x=275) and
then go back on the x axis to point 3 (x=264).
The function goes from 1 (x=262) to 3 (x=264) to 2 (x=275)

Please, run my example and you should see for yourself.