Re: Vectorizing loops

[andrewcd]

Bumping an old thread of mine with a new (similar) question.  I hope I'm not
being a pest, but I'm an occasional user at best -- I mostly work in stata,
but occasionally I need to do simulations (or huge-N stats).

My problem:  I'm trying to simulate diffusion of a thing in space, and to do
that I need to calculate the Euclidian distance between all of the nodes.  I
have it below in loop format.  it is slow enough with 1000 units, but I want
to bring it to 1 million once I get the rest of the code finished.  Any
hints on how I could vectorize this particular loop?

Many thanks, muchas gracias, asante sana.

peeps=1000


%Procedure
%1) Define Space
x = 100
y = 100
%2)Define units 
        folks = ones(peeps,1)
        %-Give these folks coordinates
        folks(:,2) = rand(peeps,1)*x;
        folks(:,3) = rand(peeps,1)*y;
%3) Define distances between dudes
for i = 1:peeps
for j = 1:peeps
        dist(i,j) = (abs(folks(i,2)-folks(j,2)).^2 +
abs(folks(i,3)-folks(j,3)).^2).^.5;
        end end

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