Build matrix with other matrices.
9 views (last 30 days)
Show older comments
Perhaps this is a simple question, but I need an answer.
If I want to build a 6x8 matrix with help of 6 other matrices, is there a smart command or function to do that? I have only built matrix with vectors so far.
Anyhow, here is my attempt so far:
A=[3 4 2; 7 2 1]
B=[2 2 1; 5 2 8]
C=[4 2 1; 3 1 2; 0 7 1]
D=[1 2 4]
F=[3; 2; 1]
G=[2; 1; 4]
blkdiag(A,B,C,D,F,G)
ans =
Columns 1 through 6
3 4 2 0 0 0
7 2 1 0 0 0
0 0 0 2 2 1
0 0 0 5 2 8
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
Columns 7 through 12
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
4 2 1 0 0 0
3 1 2 0 0 0
0 7 1 0 0 0
0 0 0 1 2 4
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
Columns 13 through 14
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
3 0
2 0
1 0
0 2
0 1
0 4
>>
I got answer, but I wonder if this is correct or not.
I would be glad if you can help me
Best regards Cillian
6 Comments
Daniel Shub
on 11 May 2012
Both Sean and I are confused about what you are asking. Does Sean's "answer" give you the result you are looking for?
Answers (2)
Daniel Shub
on 26 Apr 2012
Following on from Sean's comment, I was curious if I could do his calculation in a "cleaner" way that also uses blkdiag which Cillian seems to think is needed.
x = {A,B,C,D,F,G};
sum(reshape(cell2mat(cellfun(@(y)(blkdiag(y, zeros(6-size(y, 1), 8-size(y, 2)))), x, 'UniformOutput', false)), 6, 8, 6), 3)
15 10 8 0 0 0 0 0
18 5 11 0 0 0 0 0
5 7 1 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
EDIT The high level over view of the code is I make a 6x8xN matrix, where N is 6 because you have 6 vectors you are working with. I then sum across the 3rd dimension to get the answer. So working inside out with the code:
blkdiag(y, zeros(6-size(y, 1), 8-size(y, 2)))
produces a 6x8 matrix for any y matrix (that has size less than 6x8) where the values of y are in the top left corner of the matrix and zeros are in the remaining slots.
cellfun(@(y)(blkdiag(y, zeros(6-size(y, 1), 8-size(y, 2)))), x, 'UniformOutput', false)
produces a 1x6 cell array with each element of the cell array is a 6x8 version of the corresponding input matrices A, B, C, D, F.
cell2mat(cellfun(@(y)(blkdiag(y, zeros(6-size(y, 1), 8-size(y, 2)))), x, 'UniformOutput', false))
then converts the 1x6 cell array into a 6x48 matrix where the first 6x8 elements are from the 6x8 version of A and the next 6x8 elements are from the 6x8 version of B ...
Finally
reshape(cell2mat(cellfun(@(y)(blkdiag(y, zeros(6-size(y, 1), 8-size(y, 2)))), x, 'UniformOutput', false)), 6, 8, 6)
produces the desired 6x8x6 matrix and the final sum does the summation.
Andrei Bobrov
on 11 May 2012
z = {A,B,C,D,F,G};
out = zeros(6,8);
for jj = 1:numel(z)
[i1 j1] = size(z{jj});
out(1:i1,1:j1) = out(1:i1,1:j1) + z{jj};
end
or:
[I, J, c] = cellfun(@(x)find(x),z,'un',0);
k = reshape(cellfun(@(x)x(:),[I, J, c],'un',0),[],3);
out = accumarray(cell2mat(k(:,1:2)),cat(1,k{:,3}),[6, 8]);
1 Comment
Daniel Shub
on 11 May 2012
But you didn't use BLKDIAG. You do get points for using ACCUMARRAY, but I don't think the tag was there when I posted my answer.
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!