macros/fft.C

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#include "Riostream.h"

//          J.Adamczewski, gsi, 30 May 2012
// NOTE: to be run in Go4 GUI local command line only!
//       NEVER call this script in remote analysis process!!!
// perfroms fft on histogram of name1 using the option as explained in root TVirtualFFT:FFT
// The draw flag switches if the results are displayed each time this macro is called
// if display is switched off, the result histogram is just updated in browser and existing displays
Bool_t fft(const char* name1, Option_t*  opt = "R2C M", Bool_t draw=kTRUE)
{
   if(TGo4AbstractInterface::Instance()==0 || go4!=TGo4AbstractInterface::Instance()) {
      std::cout <<"FATAL: Go4 gui macro executed outside Go4 GUI!! returning." << std::endl;
      return kFALSE;
   }
   TString newname;
   TString fullname1 = go4->FindItem(name1);
   TObject* ob1 = go4->GetObject(fullname1,1000); // 1000=timeout to get object from analysis in ms

   if ((ob1==0) || !ob1->InheritsFrom("TH1")) {
     std::cout <<"fft could not get histogram "<<fullname1 << std::endl;
     return kFALSE;
   }

   if(ob1->InheritsFrom("TH2") || ob1->InheritsFrom("TH3")){  // 2d
      std::cout <<"fft does not support 2d/3d histogram "<<fullname1 << std::endl;
      return kFALSE;
   }

   TH1* his1=(TH1*)ob1;
   TString n1=his1->GetName();
   TString t1=his1->GetTitle();
   newname.Form("_fft_%s",opt);
   TString finalname = n1+newname;
   TString finaltitle = t1+newname;


   // do fft here:
   Int_t N = his1->GetNbinsX();
   TH1D* result = new TH1D(finalname, finaltitle,N,0,N);
   result->SetName(finalname);
   result->SetTitle(finaltitle);
   result->Reset("");
   Double_t *in = new Double_t[N];
   // since we do not know type of input histo, we copy contents to Double array:
   for(Int_t ix=0; ix<N;++ix)
   {
      in[ix]=his1->GetBinContent(ix+1);
   }
   TVirtualFFT *thefft = TVirtualFFT::FFT(1, &N, opt);
   thefft->SetPoints(in);
   thefft->Transform();
   Double_t re, im;
   for (Int_t i=0; i<N; i++) {
      thefft->GetPointComplex(i, re, im);
      result->SetBinContent(i+1,TMath::Sqrt(re*re + im*im));
   }
   result->SetDirectory(0);

   TString rname = go4->SaveToMemory("FFT", result, kTRUE);
   std::cout<< "Saved result histogram to " << rname.Data() <<std::endl;
   if(draw){
      ViewPanelHandle vpanel = go4->StartViewPanel();
      go4->DrawItem(rname, vpanel);
   }
   return kTRUE;
}