matrix manipulation

how to take matrix element (i.e row) one by one and save each new matrices in a new variable example:

original matrix: a=[2 6 7 8;4 5 3 7;9 7 6 9;5 3 1 9]

become: a1=[4 5 3 7;9 7 6 9;5 3 1 9] a2=[2 6 7 8;9 7 6 9;5 3 1 9] a3=[2 6 7 8;4 5 3 7;5 3 1 9] a4=[2 6 7 8;4 5 3 7;9 7 6 9]

Answer 1

[Andrei Bobrov]

a=[2 6 7 8;4 5 3 7;9 7 6 9;5 3 1 9]
id = ~eye(size(a));
h = arrayfun(@(i1)a(id(:,i1),:),1:size(id,2),'un',0);
[out,idxout] = min(cellfun(@(x)det(x*x.'),h))

OR

a=[2 6 7 8;4 5 3 7;9 7 6 9;5 3 1 9]
id = ~eye(size(a));
s = size(a,2);
h = zeros(s*[1 1 1] - [1 0 0]);
kt = zeros(s,1);
for j1 = 1:s
    k = a(id(:,j1),:);
    kt(j1) = det(k*k.');
    h(:,:,j1) = k;
end
[out,outidx] = min(kt)

[eri]

error:

??? Undefined command/function 'arrayfun'.

[Andrei Bobrov]

release of MATLAB ?

[Walter Roberson]

Based on the error message style, Eri must be using MATLAB 5, I think.

[eri]

@andrei bobrov

your second code seem to work fine, could you explain how it works?

@andrei bobrov and Walter Roberson

i am using matlab 7

[eri]

@andrei bobrov

can you explain your code, since i need to actually work with larger matrix and more complicated function

i don't understand from line 4 onwards

Answer 2

[Sean de Wolski]

FAQ: A1 A2 An in a loop

Don't do it. That is all.

If you explain your end goal to us we can help you find a better way.

[eri]

my goal is to find the product of the result matrices * their transpose, find its determinant, find which one has the smallest determinant, then repeat the process all over again until there is only one row left

[Jan]

@eri: And this is more efficient and more flexible, if you use dynamic indices instead of a copy to a separate variable.

[eri]

@Jan Simon

and how is that?

[Walter Roberson]

Use cell arrays, as described in that FAQ entry.

Answer 3

[eri]

can someone help me?

[Sean de Wolski]

What does:

which -all arrayfun

return? And what is the output from:

ver

at the command line?