How to set formula for N variables?

I want to use a TLinearFitter for a linear multiple regression, i.e. I am need to find parameters a_i of

 y = a_0 + a_1 * x_1 + a_2 * x_2 + ....

I know that I could use


but how can I set the formula, when there are N variables? I am looking for something like


Is this possible?

I’m not really sure what exactly you want to achieve, but if the pattern is nice and repetitive, you could try building the string with a loop, like:

[code]Int_t appends = 5;
TString str = “x[0]”;
for(Int_t i=0; i<appends; ++i)
str += Form("++x[%d]", i+1);

This code gives me the string “x[0]++x[1]++x[2]++x[3]++x[4]++x[5]” which I then feed to the SetFormula() method.