if (htotal <= 0.0) return -1.0E32; causes problems

From: Chris Jillings (chris@owl.phy.queensu.ca)
Date: Mon Apr 20 1998 - 13:33:21 MEST 

Hi all,
    I am working in the interpreter in Linux with version 2.00/00
(9 March 1998). I do the following
.L ../tools/fifty80.C
.L correlation.C
correlation("rootfile.root");  // this makes a histogram and calls
  // th function fifty80 below.

Float_t fifty80(TH1 *hi, Float_t fraction = 0.8) {
  Double_t total = 0.0;
  Int_t nBins = hi->GetNbinsX();
  Int_t i = 0;
  Stat_t htotal = hi->GetIntegral();
  printf("%f\n",htotal);
  //  if (htotal <= 0.0) return -1.0E32;
  Double_t cutoff;
  cutoff = (1.0-fraction)*htotal;
  Double_t answer;
  printf("%f\n",cutoff);
  printf("Warning: Using a grainy 50/80. Only as good as bin width.\n");


  for( i=1 ; i<=nBins ; i++) {
    total += hi->GetBinContent(i);
    printf("%d\t%f\t%f\n",i,total,cutoff);
    if (total>cutoff) break;
  }
  answer =  hi->GetBinCenter(i);
  printf("Value of %f point on histogram is %f.\n",fraction,answer);
  return answer;
}
 
The first problem is the line (now commented out) with the condition
followed  by a return statement gives the interpreter amnesia. That is to
say the interpreter can not find the value of cutoff so the routine fails.

The second problem concerns bin numbering. This routine only works when I
count from 1 to nBins. I would have excpected 0 to nBins-1. Is there
documention about where unit-offset counting is performed as opposed to
zero-offset counting?

Thanks,

Chris


=================================================================
=                                                               =
= Chris Jillings                                                =
= Department of Physics   phone/voice mail: (613) 545-6000x4805 =   
= Queen's University      fax: (613) 545-6813                   =
= Kingston, Ontario       email: chris@sno.phy.queensu.ca       =             
= Canada, K7L 3N6         web: http://snodaq.phy.queensu.ca     =
=                                                               =
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