mnbins.cxx

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// @(#)root/minuit2:$Id$
// Authors: M. Winkler, F. James, L. Moneta, A. Zsenei   2003-2005

/**********************************************************************
 *                                                                    *
 * Copyright (c) 2005 LCG ROOT Math team,  CERN/PH-SFT                *
 *                                                                    *
 **********************************************************************/

#include <math.h>

namespace ROOT {

   namespace Minuit2 {


void mnbins(double a1, double a2, int naa, double& bl, double& bh, int& nb, double& bwid) {

//*-*-*-*-*-*-*-*-*-*-*Compute reasonable histogram intervals*-*-*-*-*-*-*-*-*
//*-*                  ======================================
//*-*        Function TO DETERMINE REASONABLE HISTOGRAM INTERVALS
//*-*        GIVEN ABSOLUTE UPPER AND LOWER BOUNDS  A1 AND A2
//*-*        AND DESIRED MAXIMUM NUMBER OF BINS NAA
//*-*        PROGRAM MAKES REASONABLE BINNING FROM BL TO BH OF WIDTH BWID
//*-*        F. JAMES,   AUGUST, 1974 , stolen for Minuit, 1988
//*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*

   /* Local variables */
   double awid,ah, al, sigfig, sigrnd, alb;
   int kwid, lwid, na=0, log_;

   al = a1 < a2 ? a1 : a2;
   //     al = std::min(a1,a2);
   //     ah = std::max(a1,a2);
   ah = a1 > a2 ? a1 : a2;
   if (al == ah) ah = al + 1;

   //*-*-       IF NAA .EQ. -1 , PROGRAM USES BWID INPUT FROM CALLING ROUTINE
   if (naa == -1) goto L150;
L10:
      na = naa - 1;
   if (na < 1) na = 1;

   //*-*-        GET NOMINAL BIN WIDTH IN EXPON FORM
L20:
      awid = (ah-al) / double(na);
   log_ = int(log10(awid));
   if (awid <= 1) --log_;
   sigfig = awid*pow(10.0, -log_);
   //*-*-       ROUND MANTISSA UP TO 2, 2.5, 5, OR 10
   if (sigfig > 2) goto L40;
   sigrnd = 2;
   goto L100;
L40:
      if (sigfig > 2.5) goto L50;
   sigrnd = 2.5;
   goto L100;
L50:
      if (sigfig > 5) goto L60;
   sigrnd = 5;
   goto L100;
L60:
      sigrnd = 1;
   ++log_;
L100:
      bwid = sigrnd*pow(10.0, log_);
   goto L200;
   //*-*-       GET NEW BOUNDS FROM NEW WIDTH BWID
L150:
      if (bwid <= 0) goto L10;
L200:
      alb  = al / bwid;
   lwid = int(alb);
   if (alb < 0) --lwid;
   bl   = bwid*double(lwid);
   alb  = ah / bwid + 1;
   kwid = int(alb);
   if (alb < 0) --kwid;
   bh = bwid*double(kwid);
   nb = kwid - lwid;
   if (naa > 5) goto L240;
   if (naa == -1) return;
   //*-*-        REQUEST FOR ONE BIN IS DIFFICULT CASE
   if (naa > 1 || nb == 1) return;
   bwid *= 2;
   nb = 1;
   return;
L240:
      if (nb << 1 != naa) return;
   ++na;
   goto L20;
} /* mnbins_ */

   }  // namespace Minuit2

}  // namespace ROOT