3D Array Multiplication with 2D Matrix

Hi,

I have a 3D array of lets say 500:10:32 elements. I want to multiple the first dimension of lthis array with another 1:500 matrix. How would I do this?

Regards

[Bob Thompson]

Which 500 elements from the first matrix do you want to multiply the second matrix by? There are 320 different options.

Or are you looking to multiply all 320 sets of 500 against the new matrix?

Also, how are you looking to store your new 500 x 500 matrices?

[Anum Ahmed]

I am trying to perform the element wise multiplication of the 3D array with a second 2D array and getting the 3D array as a result where lets say row elements would be multiplied with another matrix.

Answer 1

[KALYAN ACHARJYA]

data1=rand(500,10,32);% 3D Array
data2=rand(1,500);    %1x500 mat 
result=data1(1:500,1,1)*data2;  %Multiplication

[Anum Ahmed]

Hi Kalyan,

As I was trying to perform the element wise multiplication, so I guess the following will work.

data1=rand(500,10,32);% 3D Array

data2=rand(1,500); %1x500 mat

result=data1(1:500,1,1).*data2';

After getting the answer till "result", how am I going to get back the original data1 3D matrix with first dimension point multiplied by data2?

Regards

[Bob Thompson]

If you want to replace the original matrix values with your result then you can just use the same indexing that was suggested to indicate the values you want to replace.

data1(:,1,1) = data1(:,1,1).*data2';

[KALYAN ACHARJYA]

Yes @Bob Thanks

[Bob Thompson]

Also, if you want to perform the multiplication on the entire 3D array, then the first thing that comes to mind for me is for loops, or arrayfun. There might be a way to do it without loops, but I don't know it (which doesn't say much).

for i = 1:size(data1,2)
    for j = 1:size(data1,3)
        data1(:,i,j) = data1(:,i,j).*data2';
    end
end

Answer 2

[Bruno Luong]

Simply do (R2016b or later)

data1 = data1 .* data2(:)

[Bob Thompson]

Does this automatically choose the appropriate dimension though? I would logically make the connection between 500 and 500 elements in a dimension, but that doesn't mean a computer will.

Or will it produce 500 500x10x32 arrays, one for each element of data2?

[Bruno Luong]

Yes, the length of 500 of the first dimension must match. That's all.

Answer 3

[Anum Ahmed]

Thanks all..!!!

Answer 4

[stav marzuk]

Hi i think i have the same problem, but i didnt sucssed to solve it.

I have an rgb photo with the size: 30432 29516 3

and i have a mask bw with the size 30432 29516

is it possible to multiply the two of them?

rgb .*bw

this multplication is not working, is there a solution?

Thanks in advance