How do I preallocate this loop?

 Hello

 I'm trying to make my program run faster and it suggests to preallocate this loop. Anyone know how convert this loop?
 % code
    for i = 1:1:5
       z(i) = x(zipfind - 1 + i);
    end

Thanks!

Answer 1

[Evan]

Here is the loop with preallocation:

z = zeros(5,1) % preallocation
for i = 1:1:5
     z(i) = x(zipfind - 1 + i);
end

Also, it looks as if you could possibly remove the looping altogether:

x = randi(20,20,1);
zipfind = randi(20);

zloop = zeros(5,1);
for i = 1:5
   zloop(i) = x(zipfind - 1 + i);
end

zvec = x(zipfind - 1 + (1:5));

And compare the results of zloop and zvec:

>>zvec

zvec =
    14
     4
     3
    10
    20

>> zloop

zloop =
    14
     4
     3
    10
    20

So, basically, you could just replace that entire loop with:

z = x(zipfind - 1 + (1:5));