a difficulty about fit function

From: Fengchu Zhou <zhoufc_at_iopp.ccnu.edu.cn>
Date: Thu, 15 Oct 2009 19:38:49 +0800

Hi all
  A stupid question.

  I want to get the exact expression of the equation of the landau distribution in the ROOT fit gr1->Fit(landau,"R").

   When I find in the file in this path
/Root/v5-23-02/math/mathcore/src/TMath.cxx

 i find the function in the TMath.cxx
Double_t TMath::Landau(Double_t x, Double_t mpv, Double_t sigma, Bool_t norm)

 But in this function contain the expression is puzzle me . I do not know the meaning of this sentence:
 Double_t den = ::ROOT::Math::landau_pdf( (x-mpv)/sigma );

And I can not find the landau_pdf in the file Math.h

So can anyone kindly tell me the exact expression of the landau function? And the fit par[n] location in this expression. Like gauss funtion form:
  f(x)= par[1]*exp(1/par[3] *(x-par[2])^2) where the par[n] is the fit parameter

  Best regard,
    Fengchu Received on Thu Oct 15 2009 - 13:39:06 CEST

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