matrix, using variables like a1,a2,a3,...an, minimum

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eri
eri 2012-2-17
编辑： Michael 2013-10-15
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]
then i want to find determinant from each of them * their transpose (ie: det(a1*a1')) and then find which one of them has minimum value
i have asked before and i receive this answer
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)
the problem is i don't know how this code works, and since the matrix i am going to use is different than that i use as example, i can't adjust that code

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回答（3 个）

Walter Roberson
Walter Roberson 2012-2-17
N/A
N/A 2012-2-17
eval( sprintf( 'a%d=a(%d, :), ', [1;1]*(1:size(a,1))) )
carmen
carmen 2012-2-17
ok heres a brute force version without fancy commands.
a=[2 6 7 8;4 5 3 7;9 7 6 9;5 3 1 9]
rows=size(a,1);
columns=size(a,2);
for i=1:rows
b=1:rows;
b(i)=[];
tmp=a([b],:)
eval(sprintf('a%d=tmp;',i));
determinante(i)=det(tmp*tmp');
end
min=find(determinante==min(determinante)); %gives you the index of
% determinante where the minimum values is found
i hope this works for arbitrary n*m matrices

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