How to remove pre-allocation warning in this situation

Question

When plotting a set of figures using a for loop, for example:

for ei=1:length(E),
  hnds(ei) = plot(1:nP, avgR(ei,:), [clrStr(ei),'-'] ); 
end 

There is a (the famous) warning in the code for the hnds(ei) variable:

The variable hnds(ei) appears to change size on every loop iteration. Consider pre-allocating for speed.

But when I try to pre-allocate the variable:

hnds = zeros(1,length(E));

there is another warning for this new line and in the details for pre-allocation it says:

Suggested Action: Avoid preallocating memory to a variable assigned to the output of another function.

Is there any way to remove this warning, or should just ignore it?

Answer 1

You can try iterate in reverse order to avoid the warning:

for ei=length(E):-1:1,
    hnds(ei) = plot(1:nP, avgR(ei,:), [clrStr(ei),'-'] ); 
end 

In this case you do not need to pre-allocate (i.e., no hnds = zeros(1,length(E));).

By iterating in reverse order, the array size hnds is determined in the first iteration and stays fixed throughout the iterations.

See this thread for more information.

Answer 2

Just put special %#ok comment at the end of the line and it will disable all warnings associated with this line:

hnds = zeros(1,length(E)); %#ok

You can also use special %#ok<specific1, ...> comment to disable only very specific warnings but not other ones. Check this link for furhter details.

Answer 3

You can deactivate it in Preferences:

(Matlab 2013b)

I think it is not possible to suppress this certain warning in this certain loop of a single script, just global. It's different for warnings which are displayed in the command window, they can be suppressed individually.

Edit: I was wrong.