How to preallocate an array of class in MATLAB?

Question

I have an array of objects in MATLAB and I've called their constructors in a loop:

antsNumber  = 5;
for counter = 1: antsNumber
    ant(counter) = TAnt(source, target);
end

MATLAB warns me to use preallocation to speed up the process. I do know the benefits of preallocation but I don't know how to do that for objects.

Answer 1

Here are a few options, which require that you design the class constructor for TAnt so that it is able to handle a no input argument case:

• You can create a default TAnt object (by calling the constructor with no input arguments) and replicate it with REPMAT to initialize your array before entering your for loop:

  ant = repmat(TAnt(),1,5);  %# Replicate the default object
  

  Then, you can loop over the array, overwriting each default object with a new one.

• If your TAnt objects are all being initialized with the same data, and they are not derived from the handle class, you can create 1 object and use REPMAT to copy it:

  ant = repmat(TAnt(source,target),1,5);  %# Replicate the object
  

  This will allow you to avoid looping altogether.

• If TAnt is derived from the handle class, the first option above should work fine but the second option wouldn't because it would give you 5 copies of the handle for the same object as opposed to 5 handles for distinct objects.

Answer 2

The following link might be of help:

http://www.mathworks.com/help/techdoc/matlab_oop/brd4btr.html#brd4nrh
Web archive of dead link

New link:
http://de.mathworks.com/help/matlab/matlab_oop/creating-object-arrays.html