Please help with this multiplication problem

Hi folks,

We know that a 1 x n array times an m x 1 array gives an n x m matrix. I have a 1 x n x r matrix and a m x 1 x r matrix. Is there a way to do the multiplication of the two such that it gives me an m x n x r 3D matrix?

Thanks!

Jianwei

[Matt J]

We know that a 1 x n array times an m x 1 array gives an n x m matrix.

That is not correct. Perhaps you mean an mx1 array times a 1xn array gives an mxn matrix.

[Jianwei Tu]

Yep, exactly. My bad.

Answer 1

[Matt J]

You can multiply directly. Example:

[m,n,r]=deal(3,4,2);
A=rand(m,1,r);
B=rand(1,n,r);

C=A.*B;

whos A B C

  Name      Size             Bytes  Class     Attributes

  A         3x1x2               48  double              
  B         1x4x2               64  double              
  C         3x4x2              192  double              

[Jianwei Tu]

Great!

Been using the .* for a while, but did not realize you could use it such way.

Thanks!

[Matt J]

You're welcome, but please Accept-click the answer to indicate that it worked.