src/nws_portability/Forecast/exp_smooth.c

   1 /* $Id$ */
   2
   3 #include <unistd.h>
   4 #include <stdlib.h>
   5 #include <stdio.h>
   6 #include <math.h>
   7 #include <string.h>
   8 #include <strings.h>
   9
  10 #include "fbuff.h"
  11 #include "exp_smooth.h"
  12
  13 struct exp_smooth_state
  14 {
  15         fbuff series;                   /* the series so far */
  16         fbuff time_stamps;              /* the time stamps */
  17         double last_pred;
  18         double gain;
  19 };
  20
  21 /*
  22  * init local state.  can save a copy of the pointer to the
  23  * series and time stamps, if desired
  24  */
  25 char *
  26 InitExpSmooth(fbuff series, fbuff time_stamps, char *params)
  27 {
  28         struct exp_smooth_state *state;
  29         double gain;
  30         char *p_str;
  31
  32         state = (struct exp_smooth_state *)
  33                 malloc(sizeof(struct exp_smooth_state));
  34
  35         if(state == NULL)
  36         {
  37                 return(NULL);
  38         }
  39
  40         if(params == NULL)
  41         {
  42                 free(state);
  43                 return(NULL);
  44         }
  45
  46         p_str = params;
  47         gain = strtod(p_str,&p_str);
  48
  49         /*
  50          * all functions take a series and time_stamps
  51          */
  52         state->series = series;
  53         state->time_stamps = time_stamps;
  54         state->last_pred = 0.0;
  55         state->gain = gain;
  56
  57         return((char *)state);
  58 }
  59
  60 void
  61 FreeExpSmooth(char *state)
  62 {
  63         free(state);
  64         return;
  65 }
  66
  67 void
  68 UpdateExpSmooth(char *state,
  69                 double ts,
  70                 double value)
  71 {
  72         double pred;
  73         struct exp_smooth_state *s = (struct exp_smooth_state *)state;
  74
  75         pred = s->last_pred + s->gain * (value - s->last_pred);
  76
  77         /*
  78          * if there is only one value, last pred is the first valeu in the
  79          * series
  80          */
  81         if(F_COUNT(s->series) <= 1)
  82         {
  83                 s->last_pred = F_VAL(s->series,F_FIRST(s->series));
  84         }
  85         else
  86         {
  87                 s->last_pred = pred;
  88         }
  89
  90         return;
  91 }
  92
  93 int
  94 ForcExpSmooth(char *state, double *v)
  95 {
  96         struct exp_smooth_state *s = (struct exp_smooth_state *)state;
  97
  98         *v = s->last_pred;
  99
 100         return(1);
 101
 102 }
 103
 104