list,common-lisp , Trying to multiply all elements in a list of sublists with elements in another list in lisp

## Question:

Tag: list,common-lisp

I'm trying to multiply a list with n sublists with a list with n scalars. It's supposed to work like this:

``````(kmult-matrix '((3 4 2 4) (2 5 6 9) (1 -2 8 10))   '(2 3 5))
=> ((6 8 4 8) (6 15 18 27) (5 -10 40 50))
``````

Each nth sublist is multiplied with the nth scalar in the second list. Here's what I got this far:

``````(defun kmult-matrix (m k)
(apply 'append (mapcar (lambda (x1)
(mapcar (lambda (x2)
(mapcar (lambda (x3)
(* x3 x1))
x2))
m))
k)))
``````

Which results in:

``````((6 8 4 8) (4 10 12 18) (2 -4 16 20) (9 12 6 12) (6 15 18 27) (3 -6 24 30) (15 20 10 20) (10 25 30 45) (5 -10 40 50))
``````

Hope it's ok to ask this as it is for an assigment and I have the feeling that I'm not far away from the solution. Btw, I have to use mapcar.

It's a lot easier than that. Remember that `mapcar` can take more than one list. Thus:

``````(defun kmult-matrix (m k)
(mapcar (lambda (list k)
;; inside here you get a list and
;; it's corresponding multiplier k
...)
m
k))
``````

The result from the outer map would be a list with as many elements as there are sublists `m` (and corresponding elements in `k`). Inside the lambda you do another map over `lst` that does the multiplication per element. so that inner map produces once list answer per element in the outer map.

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