3-D dot product?
3-D dot product?
(OP)
I'd like to multiply a 1-D vector by a 2-D array without using a loop. Here's what I currently have:
A = ones(10,10);
z = 1:10;
for i = 1:length(z)
result(:,:,i) = z(i)*A;
end
Is there any way to do some sort of dot product between z and A that achieves the same result?
Thanks
A = ones(10,10);
z = 1:10;
for i = 1:length(z)
result(:,:,i) = z(i)*A;
end
Is there any way to do some sort of dot product between z and A that achieves the same result?
Thanks
RE: 3-D dot product?
CODE
dot product on the columns of A:
CODE
If you want to keep z as a row/column vectorI think you will still need to loop, Although you could make a temporary variable that was padded with lots of z's...
CODE
ztemp(1:size(A,1),:) = z
result = z.*A
HTH
RE: 3-D dot product?
1. Make a 3d matrix where each page is a copy of the 2d matrix
2. Make a 3d matrix where each page is a 2d matrix filled with each value in z
3. Use ".*" to compute the product
This should be considerably quicker than the for loop for large z. Make it into a function if you are using it a lot.
CODE
A = rand(10,9);
z = [1:10];
n = length(z);
[A_rows, A_cols] = size(A);
% make a 3d version of z so that the values of z are along the 3rd dimension
z_3d = zeros(1,1,n);
z_3d(1,1,:) = z;
z_all = repmat(z_3d,[A_rows, A_cols, 1]);
% Make n copies of A in a 3d array;
A_all = repmat(A,1,1,n);
% compute the product
answer = A_all.*z_all;
--
Dr Michael F Platten
RE: 3-D dot product?