Multiply a "stack" of matrices with a "stack" of vectors
6 views (last 30 days)
Show older comments
I have a matrix 2 x 2 x n and a vector 2 x n. So basically, I have n layers of 2 x 2 matrices and n layers of vectors with 2 entries. I d like to do a matrix-vector multiplication on each layer.
I could easily do this using a for loop, but is there a way which directly supports such an operation?
0 Comments
Accepted Answer
Jos (10584)
on 4 Mar 2014
Edited: Jos (10584)
on 7 Mar 2014
One option:
n = 6
% M is your 2x2xn array of "matrices
M = rand(2,2,n)
% V is your 2xn array of "vectors"
V = rand(2,n)
fh = @(k) M(:,:,k) * V(:,k)
C = arrayfun(fh,1:n,'un',0)
C2 = cat(3,C{:})
Corrected.
3 Comments
Jos (10584)
on 7 Mar 2014
You did ask for " a way which directly supports such an operation ", not for a faster way! ;-)
To be honest, I think a straight forward for-loop is as good as the accumarray approach in this case.
James Tursa
on 7 Mar 2014
If you want speed, I would suggest looking at one of the solutions I have posted.
More Answers (1)
James Tursa
on 4 Mar 2014
Edited: James Tursa
on 7 Mar 2014
Some options in the FEX:
C-mex code:
C-mex code:
m-code:
You may need to reshape the 2 x n to a 2 x 1 x n for some of these methods to work.
Also this explicit m-code:
result = sum(bsxfun(@times,M,reshape(v,1,2,n)),2);
0 Comments
See Also
Categories
Find more on Creating and Concatenating Matrices in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!