The image you show controls the interpolation for a table field. It does not control the plotting.
If you have a function in an AFU file on the XY Function Navigator, you can use Single Math tools. These are accessed In the Function Math group on the Response Simulation Tab or in the menu at Menu, Tools, Math Operations for Functions, Basic Math, Single Math.
Lagrangian Interpolation lets you specify the order of the polynomial.
Thanks for the reply. I have getting one problem in interpolating with lagrangian interpolation with 3rd order polynomial and above. When I tried to interpolate the 3rd and higher order polynimial it is giving the zero values of the last range if interpoltion. Can you please tell why it is not taking the last range when the parameter is set to "ALL". But when I change this to "Manual Input" it is working.