Left/Right Shifts in TFormula

ROOT
1

Hi, I’m wondering if there is the functionality to shift the resulting function left or right when using TFormula. For example you have “pol3” which is c0 + x*(c1 + x*(c2 + x*c3)), but is there a simple way to obtain c0 + (x-x0)*(c1 + (x-x0)*(c2 + (x-x0)*c3)))? Obviously for a pol3 it is simple for the user to define it manually, but I am wondering more in general for polN, gaus, expo, etc.

I read the TFormula docs and it does not mention this feature, but maybe there is a trick that can achieve the desired shift?

Jean-François

2

Hi,

You would need to define an additional parameter in TFormula for doing this. The Gaus and Landau functions have already this pre-defined parameter.
For “expo” you would need to define the function your-self and not use the pre-defined function. Do something like:

TFormula f("f","[0]* exp( [1] * ( x- [2]) )");

This is not supported:

TFormula f("f"," expo( x- [2])");

Best Regards
Lorenzo