Trouble cloning histogram fitted with cloned function with latex style parameter names

Hi all,

I’ve having trouble cloning a histogram that has been fitted with a cloned function with latex style parameter names.

To be more specific, I have a template function which I clone and use to fit a histogram. I then want to clone that histogram and do things with it in a separate macro. This works fine unless the original function has parameter names that are defined in a latex style. See below for the error that appears.

Error in <TFormula::Streamer>: number of parameters computed (6) is not same as the stored parameters (5)
         templateFunc : [0]*cos([1]*x) + [2]*sin([3]*x) + [4] Ndim= 1, Npar= 6, Number= 0
 Formula expression:
List of  Variables:
Var   0                    x =    0.000000
List of  Parameters:
Par   0                  a_a =    0.000000
Par   1                a_{a} =    0.000000
Par   2                    b =    0.000000
Par   3                    c =    0.000000
Par   4                    d =    0.000000
Par   5                    e =    0.000000
Expression passed to Cling:
	Double_t TFormula____id5811689462910226460(Double_t *x,Double_t *p){ return p[0]*TMath::Cos(p[2]*x[0])+p[3]*TMath::Sin(p[4]*x[0])+p[5] ; }
Warning in <TFormula::Streamer>: number of parameters list found (6) is not same as the stored one (5) - use re-created list
(int) 1

Depending on what I do afterwards with the cloned histogram, displays can be off or things can go on to segfault.

See here for a simplified macro that reproduces the problem.

#include <TF1.h>
#include <TH1.h>
#include <TCanvas.h>

int cloneHistWithParNames(){

	auto myCanv1 = new TCanvas("myCanv1","myCanv1",200,10,1200,800);

	TF1* templateFunc = new TF1("templateFunc", "[0]*cos([1]*x) + [2]*sin([3]*x) + [4]", 0, 10);

	// templateFunc->SetParNames("a", "b", "c", "d", "e"); // <--- works
	templateFunc->SetParNames("a_{a}", "b", "c", "d", "e"); // <--- does not work

	TF1* funcClone = (TF1*) templateFunc->Clone("cloneFunc");

    int nPts = 100000;

    TH1F* myHist = new TH1F("myHist", "myHist", 100, 0, 10);
	myHist->FillRandom("templateFunc", nPts);

	funcClone->SetParameter(4, myHist->Integral("WIDTH")*.1);


	auto myCanv2 = new TCanvas("myCanv2","myCanv2",200,10,1200,800);

    TH1F* histClone = (TH1F*) myHist->Clone("cloneHist");

return 1;


Am I doing something wrong? Or is this a bug that I should report? Thanks!


The problem are the latex characters in the parameter names, which in some case can confuse the TFormula parsing (especially using the “{” brackets).
We can try to improve this, but for the time being a possible workaround is to use the copy-constructor of TF1 instead of Clone. This should avoid re-parsing the formula expression

Best Regards


Thanks Lorenzo, by copying the function and making sure not to clone the histogram I can get around this issue. (Anything else still seems to fail.)

I should also maybe mention that I don’t see this issue with TGraph. Whether that might help in solving the problem I’m not sure.

Thanks again, Nick

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