lily/least-squares.cc

   1 /*
   2   This file is part of LilyPond, the GNU music typesetter.
   3
   4   Copyright (C) 1996--2011 Han-Wen Nienhuys <hanwen@xs4all.nl>
   5
   6   LilyPond is free software: you can redistribute it and/or modify
   7   it under the terms of the GNU General Public License as published by
   8   the Free Software Foundation, either version 3 of the License, or
   9   (at your option) any later version.
  10
  11   LilyPond is distributed in the hope that it will be useful,
  12   but WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14   GNU General Public License for more details.
  15
  16   You should have received a copy of the GNU General Public License
  17   along with LilyPond.  If not, see <http://www.gnu.org/licenses/>.
  18 */
  19
  20 #include "least-squares.hh"
  21
  22 #include "warn.hh"
  23
  24 void
  25 minimise_least_squares (Real *coef, Real *offset,
  26                         vector<Offset> const &input)
  27 {
  28   Real sx = 0.0;
  29   Real sy = 0.0;
  30   Real sqx = 0.0;
  31   Real sxy = 0.0;
  32
  33   for (vsize i = 0; i < input.size ();i++)
  34     {
  35       Real x = input[i][X_AXIS];
  36       Real y = input[i][Y_AXIS];
  37       sx += x;
  38       sy += y;
  39       sqx += sqr (x);
  40       sxy += x*y;
  41     }
  42
  43   int count = input.size ();
  44
  45   *coef = 0.0;
  46   *offset = 0.;
  47
  48   Real den = (count * sqx - sqr (sx));
  49   if (!count || !den)
  50     {
  51       programming_error ("minimise_least_squares ():  Nothing to minimise\n"
  52                          "This means that vertical spacing is triggered\n"
  53                          "before line breaking\n");
  54       *coef = 0.0;
  55       *offset = count ? sy / count : 0.0;
  56     }
  57   else
  58     {
  59       *coef = (count * sxy - sx * sy) / den;
  60       *offset = (sy - (*coef) * sx) / count;
  61     }
  62 }
  63