How can I write such a large matrix?

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esraa
esraa 2015-1-11
评论： Walter Roberson 2020-3-29
thank you very much, how can I construct the matrix b, b: no. of column=20 and
no. of rows=2^20=1048576.
the first column=[0 1 0 1 0 1 ........]
the second column=[0 0 1 1 0 0 1 1 0 0 1 1 ........]
the third column=[0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 ..........]
the fourth column=[0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1..................]
and so on. instead of the following command
for j=1:20
for k=0:(2^(ns-j))-1
a((2^(j-1))+1+k*(2^j):(2^j)+k*(2^j))=1;
end
b(j,:)=a;
clear a
end
b=b';
to take less time compared with the commands I use
  2 个评论
Stephen23
Stephen23 2015-1-11
This is unreadable. Please help the other people here by formatting your text correctly. You should edit your question and use the {} Code button above the text box.
You should also read these:
http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer
http://www.mathworks.com/matlabcentral/about/answers/
Oleg Komarov
Oleg Komarov 2015-1-11
@esraa: how can you fill a 1.5L bottle with 10L? The answer is you can't. If you keep asking the same question we won't be able to help. You need to tell us what do you need those 10L to begin with, so maybe we can start filling the bottle with the first 1.5L, use it, empty the bottle, re-fill and repeat until we used all 10L.
This is block processing. You need to split your problem in subproblems, in blocks whose results can then be combined at the end.
Please reformulate you question keeping specifically my suggestion in mind.

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采纳的回答

Roger Stafford
Roger Stafford 2015-1-11
b = zeros(2^20,20);
for k = 1:20
b(:,k) = repmat([zeros(2^(k-1),1);ones(2^(k-1),1)],2^(20-k),1);
end
  4 个评论
显示 2更早的评论
John D'Errico
John D'Errico 2015-1-11
He is asking the same question OVER AND OVER AGAIN. The answer won't change. If the matrix is too big for his computer then get a faster computer. Get more memory. Use 64 bit MATLAB.
Stephen23
Stephen23 2015-1-11
编辑：Stephen23 2015-1-11
The code could also do with some improvement...

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更多回答（1 个）

Raquel Taijito
Raquel Taijito 2020-3-29
How do I create a large matrix of 96 by 96 with each element being 0.6?
  1 个评论
Walter Roberson
Walter Roberson 2020-3-29
ones(96)*0.6
If I recall correctly, there are approaches that are slightly faster but take more code. The difference in timing is small unless you have to do a lot of this.

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