cofactor.cpp

   1 // Cofactor of a matrix component.
   2
   3 #include "stdafx.h"
   4 #include "defs.h"
   5
   6 void
   7 eval_cofactor(void)
   8 {
   9         int i, j, n;
  10         push(cadr(p1));
  11         eval();
  12         p2 = pop();
  13         if (istensor(p2) && p2->u.tensor->ndim == 2 && p2->u.tensor->dim[0] == p2->u.tensor->dim[1])
  14                 ;
  15         else
  16                 stop("cofactor: 1st arg: square matrix expected");
  17         n = p2->u.tensor->dim[0];
  18         push(caddr(p1));
  19         eval();
  20         i = pop_integer();
  21         if (i < 1 || i > n)
  22                 stop("cofactor: 2nd arg: row index expected");
  23         push(cadddr(p1));
  24         eval();
  25         j = pop_integer();
  26         if (j < 1 || j > n)
  27                 stop("cofactor: 3rd arg: column index expected");
  28         cofactor(p2, n, i - 1, j - 1);
  29 }
  30
  31 void
  32 cofactor(U *p, int n, int row, int col)
  33 {
  34         int i, j;
  35         for (i = 0; i < n; i++)
  36                 for (j = 0; j < n; j++)
  37                         if (i != row && j != col)
  38                                 push(p->u.tensor->elem[n * i + j]);
  39         determinant(n - 1);
  40         if ((row + col) % 2)
  41                 negate();
  42 }