Q: How to initialize an array with a constant?

Easy, huh? Well, there are at least a few ways:

1. Most common one (on my machine it takes 0.24s):
 X=5*ones(1e6,1);

2. A better way (probably by Tim Love, tpl@eng.cam.ac.uk), which takes only 0.11s:

 X=repmat(5,1e6,1);

3. And my favorite one(0.10s)

 X=zeros(1e6,1);X(:)=5;
Note, that you can initialize selected elements with a constant as well, e.g. instead of
 Y(idx)=zeros(length(idx),1);
you can use much more elegant
 Y(idx)=0;