Add a known column to a matrix 'n' times without a loop?

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ken
ken 2011-5-22
Hi Guys!
Is there a way of qriting the script below without the loop? I'm sure there's a way but I can't find it in the help section or the internet.
I want to add a known column of numbers to a matrix 'n' times.
Thank you!
Ken
clear all
clc
a=zeros(5,6); % matrix a
[m,n]=size(a);
b=zeros(m,n); % matrix b
b(1:10)=[8 8 8 8 8 10 10 10 10 10];
for i=3:n;
b(:,i)=[1 2 3 4 5];
end
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Walter Roberson
Walter Roberson 2011-5-22
These days "for loops" are not necessarily slower, and in some cases are faster.

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2011-5-22
b(:,k:n) = (1:5)'*ones(1,n-k+1);
more
V = 1:5;
b(:,k:n) = V(ones(1,n-k+1),:).';
more more
b(:,k:n) = repmat(1:5,n-k+1,1).';
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Jan
Jan 2011-5-23
@Andrei: The ONES method is applied inside REPMAT also. Therefore I expect using it directly is faster, because the overhead of calling a function is avoided.
Usually a matrix with repeated rows wastes memory, because of the redundancy. Therefore a BSXFUN method can be faster: Do not create the matrix explicitely, but instruct BSXFUN to perform an operation by "inflating" the vector dynamically.

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更多回答（1 个）

Fangjun Jiang
Fangjun Jiang 2011-5-22
help repmat

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