leading.cpp

   1 /* Return the leading coefficient of a polynomial.
   2
   3 Example
   4
   5         leading(5x^2+x+1,x)
   6
   7 Result
   8
   9         5
  10
  11 The result is undefined if P is not a polynomial. */
  12
  13 #include "stdafx.h"
  14 #include "defs.h"
  15
  16 void
  17 eval_leading(void)
  18 {
  19         push(cadr(p1));
  20         eval();
  21         push(caddr(p1));
  22         eval();
  23         p1 = pop();
  24         if (p1 == symbol(NIL))
  25                 guess();
  26         else
  27                 push(p1);
  28         leading();
  29 }
  30
  31 #define P p1
  32 #define X p2
  33 #define N p3
  34
  35 void
  36 leading(void)
  37 {
  38         save();
  39
  40         X = pop();
  41         P = pop();
  42
  43         push(P);        // N = degree of P
  44         push(X);
  45         degree();
  46         N = pop();
  47
  48         push(P);        // divide through by X ^ N
  49         push(X);
  50         push(N);
  51         power();
  52         divide();
  53
  54         push(X);        // remove terms that depend on X
  55         filter();
  56
  57         restore();
  58 }