filter.cpp

   1 /* Remove terms that involve a given symbol or expression. For example...
   2
   3         filter(x^2 + x + 1, x)          =>      1
   4
   5         filter(x^2 + x + 1, x^2)        =>      x + 1
   6 */
   7
   8 #include "stdafx.h"
   9 #include "defs.h"
  10
  11 void
  12 eval_filter(void)
  13 {
  14         p1 = cdr(p1);
  15         push(car(p1));
  16         eval();
  17         p1 = cdr(p1);
  18         while (iscons(p1)) {
  19                 push(car(p1));
  20                 eval();
  21                 filter();
  22                 p1 = cdr(p1);
  23         }
  24 }
  25
  26 /* For example...
  27
  28         push(F)
  29         push(X)
  30         filter()
  31         F = pop()
  32 */
  33
  34 void
  35 filter(void)
  36 {
  37         save();
  38         p2 = pop();
  39         p1 = pop();
  40         filter_main();
  41         restore();
  42 }
  43
  44 void
  45 filter_main(void)
  46 {
  47         if (car(p1) == symbol(ADD))
  48                 filter_sum();
  49         else if (istensor(p1))
  50                 filter_tensor();
  51         else if (find(p1, p2))
  52                 push_integer(0);
  53         else
  54                 push(p1);
  55 }
  56
  57 void
  58 filter_sum(void)
  59 {
  60         push_integer(0);
  61         p1 = cdr(p1);
  62         while (iscons(p1)) {
  63                 push(car(p1));
  64                 push(p2);
  65                 filter();
  66                 add();
  67                 p1 = cdr(p1);
  68         }
  69 }
  70
  71 void
  72 filter_tensor(void)
  73 {
  74         int i, n;
  75         n = p1->u.tensor->nelem;
  76         p3 = alloc_tensor(n);
  77         p3->u.tensor->ndim = p1->u.tensor->ndim;
  78         for (i = 0; i < p1->u.tensor->ndim; i++)
  79                 p3->u.tensor->dim[i] = p1->u.tensor->dim[i];
  80         for (i = 0; i < n; i++) {
  81                 push(p1->u.tensor->elem[i]);
  82                 push(p2);
  83                 filter();
  84                 p3->u.tensor->elem[i] = pop();
  85         }
  86         push(p3);
  87 }