what is the best fitting tool to a data with sharp change in slop?

Hi all,

I am attaching plot of plotted data and fitted curve to this data. The figure shows deviation at regions that have sudden change in slop. The functions I used are polyfit and polyval. Is there any other fitting function or technique that gives better fitting to the curve.

Thanks in advance Aziz

[KSSV]

You have not attached any figure here. Try using spline.