Variable size changes on every iteration
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Hi,
What is an efficient way of doing the following task.
departure_time(1) = 250;
file_arrival(1) = 0.0;
for i = 2:30
departure_time(i) = arrival_time(i)+transmission_time(i)+departure_time(i-1);
end
This code is working fine for me but the matlab script editor show the message that "the variable departure_time changes size on every loop iteration. I am sure that there will be another way of achieving the same task, right?
Thank you so much.
采纳的回答
Pre-allocate. Before departure(1) = 250, place:
departure_time = NaN .* ones(30,1);
4 个评论
Aftab Ahmed Khan
2014-6-5
编辑：Aftab Ahmed Khan
2014-6-5
José-Luis
2014-6-5
The thing with Matlab is if that you don't tell it what size a variable will be, it will increase its size as long as you keep appending stuff to it, as you do in that loop.
That is very inefficient computationally: since the elements of a matrix are placed contiguously in memory, said memory needs to be reallocated when you increase the size of your array.
A way to prevent that is to tell Matlab beforehand the size the final array will have: pre-allocation.
Please accept an answer if it helped you.
Aftab Ahmed Khan
2014-6-5
José-Luis
2014-6-5
My pleasure, thank you.
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