RE: TF1 (TFormula) cannot use TMath::Landau

From: Philippe Canal <pcanal_at_fnal.gov>
Date: Tue, 12 Jul 2005 17:20:55 -0500

Hi,

I can reproduce the problem. We'll check into it.

Cheers,
Philippe.

-----Original Message-----
From: owner-roottalk_at_pcroot.cern.ch [mailto:owner-roottalk_at_pcroot.cern.ch] On Behalf Of Christian Vogel
Sent: Tuesday, July 12, 2005 10:48 AM
To: roottalk_at_pcroot.cern.ch
Subject: [ROOT] TF1 (TFormula) cannot use TMath::Landau

Hi,

I am trying to fit some more complicated function to my data but have problems combining even simple formulae in my TF1s. As a simple example, I try a landau centered at 0, constant 1, sigma 0.5, TF1 *f = new TF1("f","landau",-10,10); f->Draw() works as expected.

Now I want to do more complicated stuff, so I try to use some of the TMath::-Functions to reproduce the landau above.

Quote from http://root.cern.ch/root/html/src/TFormula.cxx.html :
> In the same way the expression "landau" is a substitute for
> [0]*TMath::Landau(x,[1],[2],kFALSE).

So I try (kFALSE gives me an error, I substitute with 0):

``` root [30] TF1 *g=new TF1("g","[0]*TMath::Landau(x,[1],[2],0)",-10,10)
root [31] g->SetParameters(1,0,0.5)
root [32] g->Draw()

```

!!! This only gives a flat line y=1 for all x in -10 .. 10. !!!

root [34] g->Print()
g : [0]*TMath::Landau(x,[1],[2],0) Ndim= 1, Npar= 3, Noper= 7

``` fExpr[0] = [0]  action = 140 action param = 0
fExpr[1] = x  action = 144 action param = 0
fExpr[2] = [1]  action = 140 action param = 1
fExpr[3] = [2]  action = 140 action param = 2
fExpr[4] = 0  action = 141 action param = 0
fExpr[5] = Double_t TMath::Landau(Double_t x,Double_t mpv=0,Double_t
```
sigma=1,Bool_t norm=kFALSE) action = 145 action param = 4  fExpr[6] = * action = 3 action param = 0 Optimized expresion
``` fExpr[0] = [0]           action = 146 action param = 0
fExpr[1] = x             action = 146 action param = 0
fExpr[2] = [1],[2],0,Double_t TMath::Landau(Double_t x,Double_t
mpv=0,Double_t sigma=1,Bool_t norm=kFALSE)               action = 149 action
param = 0
fExpr[3] = *             action = 3 action param = 0
Par  0                    p0 = 1
Par  1                    p1 = 0
Par  2                    p2 = 0.5
```

TH1.Print Name = Func, Entries= 100, Total sum= 100

What's the preferred way of fitting more complicated formulae? Always writing a compiled c-function?

root [38] gROOT->GetVersion()
(const char* 0x84d566c)"5.02/00"

Chris

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Received on Wed Jul 13 2005 - 00:28:04 MEST

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