MATLAB: How can make the Loop more efficient

errorfor looploop

I have this Loop
m=0.05;
for
i=1:1000;
     r=  poissrnd(m);
    t(1,i)= r;
end
t
there is an orange tag to right of this line "" t(1,i)=[r]; "" says ( the variable appears to change size on every loop iteration. consider preallocating for speed)
What should I do to make my loop more efficient?

Best Answer

If you preallocate the variable before the loop, the variable will not have to grow in size within the loop. Growing in size is an issue because it forces MATLAB to allocate a different memory block for the variable, copy over the data, and then delete the old memory every time. You can preallocate with:
t = zeros(1, 1000);
Of course, you could eliminate the "for" loop and just generate the array of Poisson random numbers directly:
t = poissrnd(m, 1, 1000);
-Cam
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