Fit with Heaviside function

[hvsouza]

I know this is a really old topic, but I have not found a solution (using TF1) in any search, so I am posting here what worked for me.

You can use TMath::Sign function to make the TF1 as the following:

TF1 *myHeavi = new TF1(“myHeavi”,“(1+TMath::Sign(1,x))/2”,-20,20)

And if you want the half-maximum as parameter, you can simply do:

TF1 *myHeavi = new TF1(“myHeavi”,“(1+TMath::Sign(1,x - [0]))/2”,-20,20)

Here is the link for a good explanation of the Sign function:

TMath::Sign(a,b) question

With the two argument approach, you can have the “standard” behaviour using : TMath::Sign(1, b) which returns 1 or -1 depending on the sign of b, but also you can have it return a with the same sign as b, using: TMath::Sign(a, b) as this might also be useful in several cases, like: if (TMath::Sign(iy,idy) == iy) Cheers, Fons.

I hope it helps, if there is a simpler solution please let me know.

Cheers