[Maxima-discuss] submatrix selection ala Matlab using doparse and ".."

[Richard F. <fa...@be...>]

consider mm:  genmatrix(e,3,4);
selecting rows and colums from mm
can be done by

submatrix_sel(mm,  1 .. 2, 2 ..4)

where the following lisp program defines submatrix_sel

(defmfun $submatrix_sel (mm rows cols)
   ;; rows is a list like ((mlist) 1 2 3)
   ;; similarly for cols
   ;; the elt operation is 0 based, so (mlist) is 0
   ;; should check  for rows and/or cols being single index

   (let ((r (cons '(mlist)(loop for i in (cdr rows) collect (elt mm i)))))

       (cons '($matrix)(loop for k in (cdr r) collect
             (cons '(mlist)(loop for i in(cdr cols) collect (elt k i))))) ))

;;doing some checking for single indices or non-lists or .. an exercise
;; also, incorporating this into matrix subscript operation instead of
;; being an error, a submatrix selection.