# Fitting with landau

Hiii Root Users

I would like to fit a histogram with a function which can be obtained by reflecting the landau distribution about x axis how can i do this

does anybody knows the solution…

Hi,

hist->Fit(“TMath::Landau(-x)”)

See TMath::Landau() for available parameters.

Cheers, Axel.

or even simpler h->Fit(“landau”);

Rene

Hiii Axel

I did try to fit the distribution with for example TMath::Landau(-x,0,1,0) but it says unknown function TMath::Landau(-x,0,1,0) and also tried with Fit(“landau”) but in this case it is doing with the standard landau not with the mirror reflected landau …

Is there is another alteranative to this problem

You should call the right constructor. In your case do

``` TF1 f1("f1","*TMath::Landau(-x,,)",0,1); f1.SetParameters(1,0,0.3); //for example ```
Rene

Hii Rene

Actually i first try to plot the distribution with both +x and -x so it is plotting with +x but with -x it is not plotting anything the code that is uses is as follow
TF1 *f1 = new TF1(“f1”,"*TMath::Landau(x,,)",0,100);
f1->SetParameters(1,50,5);
f1->Draw()
rd.pdf (13 KB)

of course you must set a valid range for your function. Try, eg:

```TF1 *f1 = new TF1("f1","*TMath::Landau(x,,)",-100,100); ```
Rene

Thanks Rene

Now I am getting the mirror inverted landau distribution