Hello,
I’m trying to use simplex to fit a TH1D histogram.
I did use the command at the beginning of my macro:
ROOT::Math::MinimizerOptions::SetDefaultMinimizer("Minuit", "Simplex");
to change the default algorithm to Simplex, but the fit still says that it’s using MIGRAD.
How do I correct this?
Thank you very much,
Hoa.
Please read tips for efficient and successful posting and posting code
_ROOT Version: 6.24/00
Platform: Not Provided
Compiler: Not Provided
Hello,
If you are doing it before fitting it should work and use Simplex. Can you please get the FitResult , using option “S” and then print it,
auto r = h1->Fit(function,"S");
r->Print();
Lorenzo
Hi @moneta ,
Printing the fit result gives me:
****************************************
Invalid FitResult (status = 4 )
****************************************
Minimizer is Minuit / MigradImproved
Chi2 = 3342.49
NDf = 14
Edm = 805.169
NCalls = 932
p0 = 29.3491 +/- 1.49009e-06
p1 = 3.56235 +/- 0.000171586
p2 = 344330 +/- 1397.5
p3 = 10.9942 +/- 3.60064e-05
p4 = 5 +/- 0.0012021 (limited)
p5 = 1.00004 +/- 0.0062542 (limited)
It still shows Migrad instead of Simplex.
Here are the codes I’m using, including a histogram generator[1] and fitter[2], together with a function declarations[3].
I the fitter, I set the default minimizer and algorithm to minuit and simplex at line 65, right at the start of the main code. Am I doing anything wrong?
Thank you,
Hoa.
[1] hit_generator_forum.C (1.5 KB)
[2] spectrum_fitter_forum.C (6.1 KB)
[3] function_forum.h (6.6 KB)
Hi,
You are using option "M", which is a special algorithm used after minimization to check if the minimum is really a global one. Unfortunately this algorithm does not work very well, I would eventually try in a second fit If you remove that option you should see the result of Simplex
Lorenzo