lily/least-squares.cc

   1 /*
   2   least-squares.cc -- implement minimise_least_squares
   3
   4   source file of the GNU LilyPond music typesetter
   5
   6   (c) 1996--2009 Han-Wen Nienhuys <hanwen@xs4all.nl>
   7 */
   8
   9 #include "least-squares.hh"
  10
  11 #include "warn.hh"
  12
  13 void
  14 minimise_least_squares (Real *coef, Real *offset,
  15                         vector<Offset> const &input)
  16 {
  17   Real sx = 0.0;
  18   Real sy = 0.0;
  19   Real sqx = 0.0;
  20   Real sxy = 0.0;
  21
  22   for (vsize i = 0; i < input.size ();i++)
  23     {
  24       Real x = input[i][X_AXIS];
  25       Real y = input[i][Y_AXIS];
  26       sx += x;
  27       sy += y;
  28       sqx += sqr (x);
  29       sxy += x*y;
  30     }
  31
  32   int count = input.size ();
  33
  34   *coef = 0.0;
  35   *offset = 0.;
  36
  37   Real den = (count * sqx - sqr (sx));
  38   if (!count || !den)
  39     {
  40       programming_error ("minimise_least_squares ():  Nothing to minimise\n"
  41                          "This means that vertical spacing is triggered\n"
  42                          "before line breaking\n");
  43       *coef = 0.0;
  44       *offset = count ? sy / count : 0.0;
  45     }
  46   else
  47     {
  48       *coef = (count * sxy - sx * sy) / den;
  49       *offset = (sy - (*coef) * sx) / count;
  50     }
  51 }
  52