# Using functions relating polynomial

2 views (last 30 days)
Vel Boi on 9 Dec 2019
Commented: Vel Boi on 13 Dec 2019
Hi guys,
I would like to develop a function called poly_prod which determines the product of two polynomials. Let say P=[1 1 -7 -15] and Q=[3 -1 2], and when I use poly_prod(P,Q), the following answer is expected.
First Q(1)*P, which is [3 3 -21 -45]
Second Q(2)*P, which is [-1 -1 7 15]
Third Q(3)*P, which is [2 2 -14 -30]
Then it should be added like this:
[3 3 -21 -45 0 0] + [0 -1 -1 7 15] + [0 0 2 2 -14 -30]
and the final answer should show: [3 2 -20 -36 1 -30]
Thank you.

Rik on 9 Dec 2019
What have you tried so far? It sounds like a relatively easy function to implement with a loop. And it sounds like homework, so I've added the tag.
Vel Boi on 9 Dec 2019
This is what I have done so far
function ret=poly_prod(P1,P2)
n=poly_row(P1)
m=poly_row(P2)
a=size(n)
b=size(m)
ret=[];
for n=1:b(2)
ret=[ret P1*P2(n)]
end
end
The polyrow is a function that I created to make sure the polynomial is in a row vector.
I don't know how to carry on from this.

Matt J on 9 Dec 2019
result = conv(P,Q)

#### 1 Comment

Vel Boi on 13 Dec 2019
Thanks Matt. It works.