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--2004 Han-Wen Nienhuys <hanwen@cs.uu.nl>
   7
   8  */
   9
  10 #include "least-squares.hh"
  11 #include "warn.hh"
  12
  13
  14 void
  15 minimise_least_squares (Real * coef, Real * offset,
  16                         Array<Offset> const &input)
  17 {
  18   Real sx = 0.0;
  19   Real sy = 0.0;
  20   Real sqx =0.0;
  21   Real sxy = 0.0;
  22
  23   for (int i=0; i < input.size ();i++)
  24     {
  25       Real x=input[i][X_AXIS];
  26       Real y = input[i][Y_AXIS];
  27       sx += x;
  28       sy += y;
  29       sqx += sqr (x);
  30       sxy += x*y;
  31     }
  32   int N = input.size ();
  33
  34   *coef =0.0;
  35   *offset =0.;
  36
  37   Real den = (N*sqx - sqr (sx));
  38   if (!N || !den)
  39     {
  40       programming_error ("minimise_least_squares ():  Nothing to minimise");
  41       *coef = 0.0;
  42       *offset = N ? sy/N : 0.0;
  43     }
  44   else
  45     {
  46       *coef = (N * sxy - sx*sy)/den;
  47       *offset = (sy - (*coef) * sx)/N;
  48     }
  49 }
  50