module/slib/determ.scm

   1 ;"determ.scm" Determinant
   2
   3 (define (determinant m)
   4   (define (butnth n lst)
   5     (if (zero? n) (cdr lst) (cons (car lst) (butnth (+ -1 n) (cdr lst)))))
   6   (define (minor m i j)
   7     (map (lambda (x) (butnth j x)) (butnth i m)))
   8   (define (cofactor m i j)
   9     (* (if (odd? (+ i j)) -1 1) (determinant (minor m i j))))
  10   (define n (length m))
  11   (if (eqv? 1 n) (caar m)
  12       (do ((j (+ -1 n) (+ -1 j))
  13            (ans 0 (+ ans (* (list-ref (car m) j) (cofactor m 0 j)))))
  14           ((negative? j) ans))))