Multiply each item of an array with every item of another array

Dear matlab community,

I have a relatively simple problem:

I have two arrays, say:

1

2

3

and

10

11

12

I would like to multiply each of the first vector items with every of the second vector items, and print a new vector, which gives the output:

1*10

1*11

1*12

2*10

2*11

2*12

3*10

3*11

3*12

Thank you very much, I appreciate your help!

Greetings from Australia,

Chris

Answer 1

[Image Analyst]

Like this:

m1 = [1;2;3]
m2 = [10;11;12]
out = m1 * m2'
% Make into column vector
out = out(:)

I'm sure there are probably other ways.

[Christoph Meier]

Thank you very much! That works perfectly!

Do you happen to know how to the same with sums as well?

1

2

3

and

10

11

12

ans =

1+10

1+11

1+12

2+10

2+11

...

Many thanks!

[Image Analyst]

Here's one way. You can replicate them to make 2D arrays and then do a simple addition:

m1 = [1;2;3]
m2 = [10;11;12]
m1a = repmat(m1', length(m1), 1)
m2a = repmat(m2, 1, length(m2))
out = m1a + m2a
% Make into column vector
out = out(:)

[Christoph Meier]

Thank you very much! It works perfectly again!

[Martin Adams]

It seems like it is fairly easy to run out of memory when doing this with large arrays! I tried to do this with two 90k-long vectors! How much memory would be needed?

[Image Analyst]

>> bytes = 90000*90000*8
bytes =
               64800000000
>> gigaBytes = bytes / 1e9
gigaBytes =
                      64.8

And you'd have two arrays so that would be 129 GB. That's a fair amount. You probably don't have that much spare RAM.