How to know sigma after fitting with a multifunction?

Hello Root Users,
I am using ROOT 5.34/09. I want to fit a plot in the attached root file with the macro attached. I have tried with a 12 parameter multi function and I want to know the sigma after fitting. Also, how to calculate FWHM from this function. Could anyone help me in this ?

Thanks in advance,
Anterpreet Kaur
fit.C (2.01 KB)
plot.root (48.8 KB)

Try:
h1->GetListOfFunctions()->Print();
h1->GetFunction(“g1”)->Print();
h1->GetFunction(“g1”)->GetParameter(2)
h1->GetFunction(“g1”)->GetParameter(“Sigma”)
h1->GetFunction(“total”)->Print();
h1->GetFunction(“total”)->GetParameter(…)

[quote=“Wile E. Coyote”]Try:
h1->GetListOfFunctions()->Print();
h1->GetFunction(“g1”)->Print();
h1->GetFunction(“g1”)->GetParameter(2)
h1->GetFunction(“g1”)->GetParameter(“Sigma”)
h1->GetFunction(“total”)->Print();
h1->GetFunction(“total”)->GetParameter(…)[/quote]

Thanks, for the reply.
Output of [color=#0000FF]h1->GetFunction(“total”)->Print();[/color]
##################################################
total : gaus(0)+gaus(3)+gaus(6)+gaus(9) Ndim= 1, Npar= 12, Noper= 7
fExpr[0] = gaus(0) action = 110 action param = 0
fExpr[1] = gaus(3) action = 110 action param = 3
fExpr[2] = + action = 1 action param = 0
fExpr[3] = gaus(6) action = 110 action param = 6
fExpr[4] = + action = 1 action param = 0
fExpr[5] = gaus(9) action = 110 action param = 9
fExpr[6] = + action = 1 action param = 0
Optimized expression
fExpr[0] = gaus(0) action = 110 action param = 0
fExpr[1] = gaus(3) action = 110 action param = 3
fExpr[2] = + action = 1 action param = 0
fExpr[3] = gaus(6) action = 110 action param = 6
fExpr[4] = + action = 1 action param = 0
fExpr[5] = gaus(9) action = 110 action param = 9
fExpr[6] = + action = 1 action param = 0
Par 0 p0 = 8.2099
Par 1 p1 = 0.740543
Par 2 p2 = 0.0620684
Par 3 p3 = 697.201
Par 4 p4 = 1.00438
Par 5 p5 = 0.0547297
Par 6 p6 = 309.264
Par 7 p7 = 1.02128
Par 8 p8 = 0.0800667
Par 9 p9 = 5.29382
Par 10 p10 = 1.3149
Par 11 p11 = 0.137412
##################################################
But [color=#0000FF]h1->GetFunction(“total”)->GetParameter(Sigma)[/color] gives :
Error in TF1::TFormula: Parameter Sigma not found

So out of 12 parameters, which will give sigma for total function ?

Your “total” is a sum of four gaussian functions. Each gaussian has it’s own three parameters. There is no “common” sigma.
You can try to play with: TF1::Moment, TF1::CentralMoment, TF1::Mean, TF1::Variance

[quote=“Wile E. Coyote”]Your “total” is a sum of four gaussian functions. Each gaussian has it’s own three parameters. There is no “common” sigma.
You can try to play with: TF1::Moment, TF1::CentralMoment, [url=https://root.cern.ch/root/html534/TF1.html#TF1:Mean]TF1::Mean[/url, TF1::Variance[/quote]

I have to fit the distribution with a gaussian function and to use its sigma in some calculation. As it is not possible in the case with four gaussian functions, is there any other way to fit with one gaussian and find sigma ?