how to creat a 0and 1 matrix by another matrix

Question

Junw 2014-6-3

回答： Niklas Nylén 2014-6-3

example: I have one random number matrix a. a=[2 3 4 5 ],and then I want to use a matrix to create another matrix b depending on a.

b=[1 1 0 0 0 1 1 1 1 0 0 0 0 0].The elements in a is to describe the number of 0 and 1 in matrix b.

Please don't use for loop,it's too slow.

Answer 1

Niklas Nylén 2014-6-3

"Please don't use for loop,it's too slow." In which context are you using the function if the following code is too slow?

If a has length 10000 this code will run in 0.009 s on my computer:

tic
b = ones(1,sum(a));
acumsum = cumsum(a);
for ii = 2:2:length(a)
    b(acumsum(ii-1)+1:acumsum(ii))=0;
end
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