Construct Power of Matrix without for loop
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Hi, everyone:
Suppose I have a 2 by 2 matrix A, if I want construct a larger matrix B that is defined as:
B=[A, A^2, A^3, A^4, ... A^N];
is it possible to do it without for loop?
Thanks
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Azzi Abdelmalek
il 11 Ago 2013
Modificato: Azzi Abdelmalek
il 11 Ago 2013
Example
A=magic(2);
N=3;
B=cell2mat(arrayfun(@(x) A^x,1:N,'un',0))
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Più risposte (2)
Jan
il 12 Ago 2013
Azzi's suggestion is fine for N=3. If you are talking about larger N, neither the repeated power operator nor arrayfun nor cell2mat are efficient:
N = 10000
A = rand(2, 2);
tic;
B = cell2mat(arrayfun(@(x) A^x,1:N,'un',0));
toc
tic;
B = zeros(2, 2, N);
P = 1;
for k = 1:N
P=P*A;
B(:,:,k) = P;
end
B = reshape(B, 2, N * 2);
toc
Elapsed time is 0.199776 seconds.
Elapsed time is 0.039983 seconds.
So I'd prefer the more efficient FOR loop.
2 Commenti
Ming
il 11 Ago 2013
Modificato: Ming
il 11 Ago 2013
1 Commento
Walter Roberson
il 11 Ago 2013
Note: arrayfun() just hides the "for" loop. If you are willing to use it, then Azzi's example does what you ask.
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