MATLAB Central Newsreader - combinations of N matrixes taken K at a time

combinations of N matrixes taken K at a time

tirinacria CICCIOCICCIO — Sun, 11 Oct 2009 16:21:02 -0400

Hey I’m a new user.
I want to perform this:

I have 6 square matrixes A B C D E F
I want to find the possible combinations of these matrixes taken 3 at a time and calculate the product of the determiner of each combination
In order to find all possible combinations I can do this:
MAT={‘A’,’B’,’C’,’D’,’E’,’F’}
comb=nchoosek(MAT,3)
The results is:

comb =

    'A' 'B' 'C'
    'A' 'B' 'D'
    'A' 'B' 'E'
    'A' 'B' 'F'
    'A' 'C' 'D'
    'A' 'C' 'E'
    'A' 'C' 'F'
    'A' 'D' 'E'
    'A' 'D' 'F'
    'A' 'E' 'F'
    'B' 'C' 'D'
    'B' 'C' 'E'
    'B' 'C' 'F'
    'B' 'D' 'E'
    'B' 'D' 'F'
    'B' 'E' 'F'
    'C' 'D' 'E'
    'C' 'D' 'F'
    'C' 'E' 'F'
    'D' 'E' 'F'
Then I know all combinations

Now I want to create with a for cycle a matrix with like this:

Det=[|A|*|B|*|C| , | A|*|B|*D|,………]
How can I perform this multiplication?
The problem is that in the matrix comb, A is a text.
Please give me some advice
Thanks

Re: combinations of N matrixes taken K at a time

Matt Fig — Sun, 11 Oct 2009 16:50:24 -0400

Store your matrices in a cell array, then use nchoosek with numeric arguments to index into the cell.

A = {rand(2) rand(2) rand(2)}
t = nchoosek(1:3,2)

G = cell(size(t,1),1);
for ii = 1:size(t,1)
G = A(t,ii,1) * A(t,ii,2); % Or whatever here.
end

Re: combinations of N matrixes taken K at a time

Matt Fig — Sun, 11 Oct 2009 16:56:04 -0400

Sorry, that should read:

A = {rand(2) rand(2) rand(2)}
t = nchoosek(1:3,2)

G = cell(size(t,1),1);
for ii = 1:size(t,1)
G{ii} = A{t(ii,1)} * A{t(ii,2)}; % Or whatever here.
end

Re: combinations of N matrixes taken K at a time

Bruno Luong — Sun, 11 Oct 2009 17:46:04 -0400

"tirinacria CICCIOCICCIO" <d.accorso@tin.it> wrote in message <hat0le$jeq$1@fred.mathworks.com>...

> The problem is that in the matrix comb, A is a text.

When you call nchoosek, you can supply any kind of arrays or cell arrays. Example:

A = rand(5);
B = rand(5);
C = rand(5);
D = rand(5);
E = rand(5);
F = rand(5);

allmystuff = {A B C D E F};

threestuff = nchoosek(allmystuff, 3);

% Each row of the result THREESTUFF is one combination

If you want to compute the product of determinants, then feed NCHOOSEK with the array of determinants of A, B, ..., F, then compute PROD of the result along the second dimension.

Bruno

Re: combinations of N matrixes taken K at a time

tirinacria CICCIOCICCIO — Sun, 11 Oct 2009 17:59:03 -0400

thank you very much!