# How to plot generalized hypergeometric function in ROOT?

1. May 4, 2017

### Sandeep Hundal

Hello everyone
I am trying to write code in ROOT.I want to plot generalized hypergeometric function pFq with p=0 and q=3 i.e I want to plot 0F3(;4/3,5/3,2;x) as a function of x using TF1 class.I am not getting how to plot this function in ROOT.Kindly help me out.

2. May 5, 2017

3. May 6, 2017

### ChrisVer

Can you be more specific on which part you find difficult?
Is it generating the function? (how you define the TF1 and its parameters)
or is it drawing a TF1?

4. May 6, 2017

### ChrisVer

if it's the second, have a look at TF1::Draw()...
If it is the first, then either find a closed form that your function corresponds to (to be honest I wasn't able to find a clear answer to what that function is equal to) or make approximations (you can never have infinite sums), keeping eg the first 3 terms or 4 terms and so on (depending on what you want to do with it)....
Why would you want to use ROOT for that?

5. May 9, 2017

### Sandeep Hundal

I am not able to generate the hypergeometric function of form 0F3(;4/3,5/3,2;x).The value of function contains limit from n=0 to n=infinity.I am not able to find this function in already defined function in root.

6. May 9, 2017

### Sandeep Hundal

I need to use root because the function I need to plot contains hypergeometric function and I need to do fitting of the parameters with experimental data.Previously ,I have used ROOT only for fitting in my analysis.So ,I was trying if I can find some way to plot this function in ROOT only.

7. May 10, 2017

### Staff: Mentor

A custom PDF in RooFit could work. You don't need a sum-free closed form for the function that way, you just need a function that can be evaluated for every argument. If you fit data to it, it will take quite some time.