# how to multiply values between arrays columns to rows and generate a new vector form each of the multiplication?

2 views (last 30 days)
Seba.V on 22 Aug 2019
Commented: Star Strider on 22 Aug 2019
given x= [ 1 1 1 ] and y=[ 1 2 3 ] how can I generate a code that will multiply each column value of x by each row of y and sote this values in a new array? How can I at the same time add a zero for every new array generated at the beginning (and end) of these vectors so that i can then add all of these vectors together?
ie:
x= [ 1 1 1 ] and y=[ 1 2 3 ]
x1=[1 2 3 0 0]
x2=[0 1 2 3 0]
x3=[0 0 1 2 3 ]
x4=x1+x2+x3
answer: x4=[1 3 6 5 3 ]
I hope my question is clear enough.

Star Strider on 22 Aug 2019
The operation you are looking for is not actually multiplication, it is convolution.
Example:
x = [ 1 1 1 ];
y = [ 1 2 3 ];
z = conv(x, y)
producing:
z =
1 3 6 5 3
as you describe yoiu want.
See the documentation on the conv function (and related links) for details.

Seba.V on 22 Aug 2019
That's great thank you!
May I ask if it possible to add zeros to either side of an array (end or start) without overwrite the array values? I mean just expand the vector and be able to shift a set of values between the zeros?
like
x=[1 2 3]
x1=[ 0 1 2 3 0 0 0]
x2= [ 0 0 1 2 3 0 0]
x3=[ 0 0 0 1 2 3 0]
Star Strider on 22 Aug 2019
My pleasure!
What you want to do is what the conv function does internally.
To do what you describe, try this:
x1 = zeros(1,6);
x2 = x1;
x3 = x1;
x1((1:3)+1) = y
x2((1:3)+2) = y
x3((1:3)+3) = y
producing:
x1 =
0 1 2 3 0 0
x2 =
0 0 1 2 3 0
x3 =
0 0 0 1 2 3
z = x1 + x2 + x3
to get:
z =
0 1 3 6 5 3
Experiment to get the result you want.