Create a matrix example as per Francis' email.

[gheber]

;; Create a random matrice 4 x 6 of "density" 0.3 with |terms| <= 10:

(setf mtrx (mat-aleat 4 6 0.3 10))

========== MATRIX 4 row(s) + 6 column(s) ===== R1=[C1=1] R2=[C1=-3][C5=9] R3= R4=[C2=4][C3=3][C4=-8][C5=-7] ========== END-MATRIX

;; Only & non-null term on the row 1, namely a 1 in column 1. ;; Two non-null terms in row 2, 4 in row 4, the row 3 is null. ;; Travelling in a matrix is conveniently done by P-DISP. ;; Going to the first fake-term of LEFTCOL :

CL-USER(6): (disp-p (setf p (aref (leftcol mtrx) 1))) ((1 0 NIL) (1 1 1) (0 0 NIL))

;; means it is a term in position 1-0, it is fake (nil). ;; the "lefthand" term is in position 1-1, its value is 1: ;; the above term is in position 0-0, it is fake.

;; going to the term in position 1-1:

(disp-p (setf p (left p))) ((1 1 1) (1 0 NIL) (0 1 NIL))

;; the term is in position 1-1, its lefthand term is the ;; starting point in position 1-0, the above term is ;; in position 0-1, it is fake.

;; Running through the row 4 :

(disp-p (setf p (aref (leftcol mtrx) 4))) ((4 0 NIL) (4 5 -7) (3 0 NIL)) (disp-p (setf p (left p))) ((4 5 -7) (4 4 -8) (2 5 9)) (disp-p (setf p (left p))) ((4 4 -8) (4 3 3) (0 4 NIL)) (disp-p (setf p (left p))) ((4 3 3) (4 2 4) (0 3 NIL)) (disp-p (setf p (left p))) ((4 2 4) (4 0 NIL) (0 2 NIL)) (disp-p (setf p (left p))) ((4 0 NIL) (4 5 -7) (3 0 NIL))

;; We are back to the fake term in position 4-0

;; Running through the column 5:

(disp-p (setf p (aref (uplig mtrx) 5))) ((0 5 NIL) (0 4 NIL) (4 5 -7)) (disp-p (setf p (up p))) ((4 5 -7) (4 4 -8) (2 5 9)) (disp-p (setf p (up p))) ((2 5 9) (2 1 -3) (0 5 NIL)) (disp-p (setf p (up p))) ((0 5 NIL) (0 4 NIL) (4 5 -7))

;; "Both" terms in position 0-0 are the same and are fake.

(eq (aref (leftcol mtrx) 0) (aref (uplig mtrx) 0)) T (disp-p (aref (leftcol mtrx) 0)) ((0 0 NIL) (0 6 NIL) (4 0 NIL))

;; it's one of the standard structures to implement ;; sparse matrices.