I want to get the interpolated value of a function which depends on 3 variables , instead of just one. I know I can use the Eval function for TGraphs incase the function depends only on one variable. I also looked at the Interpolator method in TMath , but i think that is also for functions that depend on one variable.

                                                 -thanks debdatta.

If your function is a TF3 you can call the Eval(x,y,z) function.