function answer = optimize_group_distance(M)

% find all iid
% sort iid's from smallest to largest
% find differences BETWEEN all iid's
% 

% finds the break (the biggest jump) in the list of iid's
% Created by Jim Work, University of South Carolina, August 13, 2003


iidlist = [];

for i = 1:size(M,1)
   for j = 1:size(M,1)
      iidlist = [iidlist;dist3d(M(i,2), M(i,3), M(i,4), M(j,2), M(j,3), M(j,4))];
   end
end

foundone = 0;
p = sort(iidlist)
groupbreak = 0;
for i = 1:(size(p,1)-1)
   diff = (p(i+1)-p(i))
   if ((diff > p(i)) and (p(i)>1))
      groupbreak = p(i);
      foundone = 1
      diff
   end   
end

if foundone == 0
   groupbreak = diff;
end


answer = groupbreak/2;