Problem fitting with a Voigt function

ROOT
1

Hi,

I am trying to make a fit with the Voigt function, but it always gives some errors.

I have tried these alternatives:

TF1 *vfit;

(1) vfit = new TF1(“vfit”, “voigt”, 0., 180.);
(2) vfit = new TF1(“vfit”, “Voigt”, 0., 180.);
(3) vfit = new TF1(“vfit”, “TMath::Voigt”, 0., 180.);
(4) vfit = new TF1(“vfit”, “TMath::voigt”, 0., 180.);
(5) vfit = new TF1(“vfit”, TMath::Voigt, 0., 180.);
(6) vfit = new TF1(“vfit”, TMath::voigt, 0., 180.);

h1LatScat->Fit(vfit, “RS”);
vfit->SetLineColor(3);
vfit->Draw(“same”);

The alternatives (1), (2), (3), (4) compile (make), but when I run the file it gives:
Error in TFormula::Compile: Bad numerical expression : "voigt"
Error in TF1::TF1: function: vfit/voigt has 0 parameters instead of 1
Error in : function is zombie

The alternatives (5), (6) don’t compile and give the error that the expressions are ambiguous:
call of overloaded ‘TF1(const char [5], Double_t (&)(Double_t, Double_t, Double_t, Int_t), double, double)’ is ambiguous
/home/micaela/root/include/TF1.h:98: note: candidates are: TF1::TF1(const char*, ROOT::Math::ParamFunctor, Double_t, Double_t, Int_t)
/home/micaela/root/include/TF1.h:94: note: TF1::TF1(const char*, Double_t ()(const Double_t, const Double_t*), Double_t, Double_t, Int_t)
/home/micaela/root/include/TF1.h:93: note: TF1::TF1(const char*, Double_t ()(Double_t, Double_t*), Double_t, Double_t, Int_t)

The most curious fact about all of this is if I use:
vfit = new TF1(“vfit”, “gaus”, 0., 180.);
It runs wonderfully…

Thanks in advance,
Micaela

2

Could you provide the shortest possible running script and data file reproducing your problem? (as attachments)

Rene

3

Hi and thanks for the reply.

Well, as an attachment is my code in a “small” version… I can’t send any data because the smallest file has 120 MB. The data is produced in Geant4 and corresponds to a 18-MeV proton beam scattered by a water target and I want to fit a Voigt profile to the angular distribution of this scattering.

Thanks in advance, once again,
Micaela
p_for_sending.cpp (11.4 KB)

4

Since I have similar problem, I will post here.

Questio nis, how to use Voigt function and/or how to correctly define predefined function (e.g. gaus, pol1, exp, etc.).

Here is my code

[code]
#include <TMath.h>
#include <TF1.h>

Double_t funVoigt(Double_t *x, Double_t *par) {
return par[0] * TMath::Voigt(x[0] - par[1], par[2], par[3], 4);
}

int main()
{
TROOT AnalysisDST_Cal1(“Analysis”,“compiled analysis macros”);
TApplication app(“test”, NULL, NULL, NULL, 0);

TF1 * bkg = new TF1("bkg", "pol1", 1095, 1150);
TF1 * fVoigt = new TF1("voigt", funVoigt, 1095, 1150, 4);

TF1 * ftot1 = new TF1("f_total1", "gaus+bkg", 1095, 1150);
TF1 * ftot2 = new TF1("f_total2", "voigt+bkg", 1095, 1150);

printf("\n\ngaus + pol1");
ftot1->Print();
printf("npar1 = %d\n", ftot1->GetNpar());

printf("\n\nvoigt + pol1");
ftot2->Print();
printf("npar2 = %d\n", ftot2->GetNpar());

} [/code]

and here is the output:

[code]Error in TFormula::Compile: Empty String
Error in TF1::TF1: function: f_total2/voigt+bkg has 0 parameters instead of 1

gaus + pol1 f_total1 : gaus+bkg Ndim= 1, Npar= 5, Noper= 3
fExpr[0] = gaus action = 110 action param = 0
fExpr[1] = pol1 action = 130 action param = 101
fExpr[2] = + action = 1 action param = 0
Optimized expression
fExpr[0] = gaus action = 110 action param = 0
fExpr[1] = pol1 action = 130 action param = 101
fExpr[2] = + action = 1 action param = 0
Par 0 p0 = 0
Par 1 p1 = 0
Par 2 p2 = 0
Par 3 p3 = 0
Par 4 p4 = 0
npar1 = 5

voigt + pol1 f_total2 : voigt+bkg Ndim= 0, Npar= 0, Noper= 0
npar2 = 0[/code]

First we see that there is some error when defining function, so second problem is related to the first problem, that there is no correcte “voigt + pol1” function. How to do it correctly?

5

Search for the string “TF1 objects can reference” in the TF1 class description (see also the TFormula::Analyze method description).

6

Oh, I missed that I am of type C… Thanks!

7

Hi,
I know it is a very old topic, but I have exactly the same problem…I used your (1) and got the same errors as you did:

Error in TFormula::Compile: Bad numerical expression : “voigt”
Error in TF1::TF1: function: vfit/voigt has 0 parameters instead of 1
Error in : function is zombie

how did you solve it?