src/math/tukey-hinges.c

   1 /* PSPP - a program for statistical analysis.
   2    Copyright (C) 2008, 2009, 2011 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>. */
  16
  17 #include <config.h>
  18
  19 #include "math/tukey-hinges.h"
  20
  21 #include <math.h>
  22
  23 #include "libpspp/assertion.h"
  24 #include "libpspp/cast.h"
  25 #include "math/order-stats.h"
  26
  27 #include "gl/xalloc.h"
  28
  29 void
  30 tukey_hinges_calculate (const struct tukey_hinges *th, double hinge[3])
  31 {
  32   double a[3];
  33   double a_star[3];
  34   int i;
  35   const struct order_stats *os = &th->parent;
  36
  37   for (i = 0 ; i < 3 ; ++i)
  38     {
  39       a_star[i] = os->k[i].tc - os->k[i].cc;
  40       a[i] = a_star[i] / os->k[i].c_p1;
  41
  42       if (a_star[i] < 1)
  43         {
  44           if (os->k[i].c_p1 >= 1)
  45             {
  46               hinge[i] = (1 - a_star[i]) * os->k[i].y
  47                 + a_star[i] * os->k[i].y_p1;
  48             }
  49           else
  50             {
  51               hinge[i] = (1 - a[i]) * os->k[i].y
  52                 + a[i] * os->k[i].y_p1;
  53             }
  54         }
  55       else
  56         {
  57           hinge[i] = os->k[i].y_p1;
  58         }
  59
  60     }
  61 }
  62
  63 static void
  64 destroy (struct statistic *s)
  65 {
  66   struct tukey_hinges *th = UP_CAST (s, struct tukey_hinges, parent.parent);
  67   free (th);
  68 };
  69
  70 struct tukey_hinges *
  71 tukey_hinges_create (double W, double c_min)
  72 {
  73   double d;
  74   struct tukey_hinges *th = XZALLOC (struct tukey_hinges);
  75   struct order_stats *os = &th->parent;
  76   struct statistic *stat = &os->parent;
  77
  78   assert (c_min >= 0);
  79
  80   os->n_k = 3;
  81   os->k = th->k;
  82
  83   if (c_min >= 1.0)
  84     {
  85       d = floor ((W + 3) / 2.0) / 2.0;
  86
  87       os->k[0].tc = d;
  88       os->k[1].tc = W/2.0 + 0.5;
  89       os->k[2].tc = W + 1 - d;
  90     }
  91   else
  92     {
  93       d = floor ((W/c_min + 3.0)/ 2.0) / 2.0 ;
  94       os->k[0].tc = d * c_min;
  95       os->k[1].tc = (W + c_min) / 2.0;
  96       os->k[2].tc = W + c_min * (1 - d);
  97     }
  98
  99
 100   stat->destroy = destroy;
 101
 102   return th;
 103 }